Systems and methods of using ssl pools for wan acceleration

ABSTRACT

The present invention is directed towards systems and methods for using a Secure Socket Layer (SSL) session from a pool of SSL sessions shared between intermediaries. The method includes receiving, by a first intermediary, information on one or more SSL sessions of a pool established by a second intermediary with a server. The first intermediary can be in communication with one or more clients and the second intermediary can be in communication with one or more servers. The first intermediary may receive a request from a client to establish an SSL session with the server. The first intermediary can identify an SSL session from the pool of SSL sessions. The first intermediary may establish the SSL session with the client responsive to the request.

FIELD OF THE DISCLOSURE

The present application generally relates to data communicationnetworks. In particular, the present application relates to systems andmethods of using Secure Socket Layer (SSL) pools for wan acceleration.

BACKGROUND

End-to-end secure communications between a client and a server may beprovided by an SSL session connection. The connection may be establishedacross one or more intermediaries, such as network appliances, betweenthe client and the server. A single intermediary between a client and aserver may facilitate establishment of an SSL session connection,providing shielding protection to the client via a virtual privatenetwork (VPN) for example. In some cases, there are multipleintermediaries, for example for providing data acceleration and otherservices between two intermediaries across one or more networks. Thefirst intermediary may be in communication with one or more clientswhile the second intermediary may be in communication with one or moreservers.

BRIEF SUMMARY

The present application is directed to methods and systems for using aSecure Socket Layer (SSL) session from a pool of SSL sessions associatedwith one or both intermediaries between a client and a server. A firstintermediary may request a secure connection with a second intermediaryon behalf of the client. The second intermediary may maintain or provideone or more SSL sessions with a server that is in turn associated withone or more SSL session state machines. An SSL pool manager may managethe one or more SSL session state machines on behalf of the secondintermediary. A plurality of SSL sessions associated with the secondintermediary may be collectively referred to as a SSL session pool. Asignal tunnel or channel can be established between the first and secondintermediaries for authentication and/or communicating information aboutthe SSL session pool. Based on the information about the SSL sessionpool, the pool manager may identify an SSL session from the SSL sessionpool for establishment of an SSL session between the server and theclient.

In one aspect, the present invention is related to a method for using aSecure Socket Layer (SSL) session from a pool of SSL sessions sharedbetween intermediaries. The method includes receiving, by a firstintermediary, information on one or more SSL sessions of a poolestablished by a second intermediary with a server. The firstintermediary may be in communication with one or more clients and thesecond intermediary may be in communication with one or more servers.The first intermediary may receive a request from a client to establishan SSL session with the server. The first intermediary may also identifyan SSL session from the pool of SSL sessions. The first intermediary mayestablish the SSL session with the client responsive to the request.

In some embodiments, the secondary intermediary may establish apredetermined one or more SSL sessions with the server to form the pool.The secondary intermediary may establish one or more SSL sessions witheach of a plurality of servers for one or more pools of SSL sessions.The secondary intermediary may further forward to the first intermediaryinformation on the one or more SSL sessions of the pool. The firstintermediary can query from the second intermediary information on theone or more SSL sessions of the pool. The first intermediary may alsoreceive session specific data for the one or more SSL sessions of thepool.

In one embodiment, the first intermediary intercepts the request of theclient communicated to the server. The first intermediary may request anavailable SSL session from the pool of one or more SSL sessions. Thefirst intermediary may also determine an available SSL session from theinformation on the one or more SSL sessions of the pool. In someembodiments, the first intermediary may identify to the secondintermediary, use of the SSL session from the pool of one or more SSLsessions.

In another aspect, a system for using a Secure Socket Layer (SSL)session from a pool of SSL sessions shared between intermediariesincludes a first intermediary receiving information on one or more SSLsessions of a pool of SSL sessions. The first intermediary may be incommunication with one or more clients. A second intermediary may be incommunication with one or more servers. The second intermediary cancommunicate the information on the one or more SSL sessions of the poolof SSL sessions established by the second intermediary. The firstintermediary may receive a request from a client to establish an SSLsession with the server. The first intermediary may also identify an SSLsession from the pool of SSL sessions. Further, the first intermediarymay establish the SSL session with the client responsive to the request.

In some embodiments, the secondary intermediary establishes apredetermined one or more SSL sessions with the server to form the pool.The second intermediary may establish one or more SSL sessions with eachof a plurality of servers for one or more pools of SSL sessions. Thefirst intermediary can query from the second intermediary information onthe one or more SSL sessions of the pool. The first intermediary mayreceive session specific data for the one or more SSL sessions of thepool. In one embodiment, the first intermediary can intercept therequest of the client communicated to the server.

In one embodiment, the first intermediary requests an available SSLsession from the pool of one or more SSL sessions. The firstintermediary may determine an available SSL session from the informationon the one or more SSL sessions of the pool. The first intermediary mayidentify to the second intermediary use of the SSL session from the poolof one or more SSL sessions. The first intermediary can communicate withone or more clients via a first local network. In addition, the secondintermediary may communicate with the one or more servers via a secondlocal network. In some embodiments, the first intermediary and secondintermediary communicates via a wide area network.

The details of various embodiments of the invention are set forth in theaccompanying drawings and the description below.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other objects, aspects, features, and advantages ofthe invention will become more apparent and better understood byreferring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a block diagram of an embodiment of a network environment fora client to access a server via one or more network optimizationappliances;

FIG. 1B is a block diagram of another embodiment of a networkenvironment for a client to access a server via one or more networkoptimization appliances in conjunction with other network appliances;

FIG. 1C is a block diagram of another embodiment of a networkenvironment for a client to access a server via a single networkoptimization appliance deployed stand-alone or in conjunction with othernetwork appliances;

FIGS. 1E and 1F are block diagrams of embodiments of a computing device;

FIG. 2A is a block diagram of an embodiment of an appliance forprocessing communications between a client and a server;

FIG. 2B is a block diagram of another embodiment of a client and/orserver deploying the network optimization features of the appliance;

FIG. 3 is a block diagram of an embodiment of a client for communicatingwith a server using the network optimization feature;

FIG. 4A is a block diagram of an embodiment of a system using a SecureSocket Layer (SSL) session from a pool of SSL sessions shared betweenintermediaries;

FIG. 4B is a block diagram of an embodiment of a state machine for anowned pool of an intermediary;

FIG. 4C shows embodiments of state machines for an SSL state machineidentifier; and

FIG. 4D is a flow diagram of an embodiment of a method for using aSecure Socket Layer (SSL) session from a pool of SSL sessions sharedbetween intermediaries.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements.

DETAILED DESCRIPTION

For purposes of reading the description of the various embodiments ofthe present invention below, the following descriptions of the sectionsof the specification and their respective contents may be helpful:

-   -   Section A describes a network environment and computing        environment useful for practicing an embodiment of the present        invention;    -   Section B describes embodiments of a system and appliance        architecture for accelerating delivery of a computing        environment to a remote user;

Section C describes embodiments of a client agent for acceleratingcommunications between a client and a server; and

Section D describes embodiments of systems and methods for using an SSLsession from a pool of SSL sessions shared between intermediaries.

A. Network and Computing Environment

Prior to discussing the specifics of embodiments of the systems andmethods of an appliance and/or client, it may be helpful to discuss thenetwork and computing environments in which such embodiments may bedeployed. Referring now to FIG. 1A, an embodiment of a networkenvironment is depicted. In brief overview, the network environment hasone or more clients 102 a-102 n (also generally referred to as localmachine(s) 102, or client(s) 102) in communication with one or moreservers 106 a-106 n (also generally referred to as server(s) 106, orremote machine(s) 106) via one or more networks 104, 104′, 104″. In someembodiments, a client 102 communicates with a server 106 via one or morenetwork optimization appliances 200, 200′ (generally referred to asappliance 200). In one embodiment, the network optimization appliance200 is designed, configured or adapted to optimize Wide Area Network(WAN) network traffic. In some embodiments, a first appliance 200 worksin conjunction or cooperation with a second appliance 200′ to optimizenetwork traffic. For example, a first appliance 200 may be locatedbetween a branch office and a WAN connection while the second appliance200′ is located between the WAN and a corporate Local Area Network(LAN). The appliances 200 and 200′ may work together to optimize the WANrelated network traffic between a client in the branch office and aserver on the corporate LAN.

Although FIG. 1A shows a network 104, network 104′ and network 104″(generally referred to as network(s) 104) between the clients 102 andthe servers 106, the clients 102 and the servers 106 may be on the samenetwork 104. The networks 104, 104′, 104″ can be the same type ofnetwork or different types of networks. The network 104 can be alocal-area network (LAN), such as a company Intranet, a metropolitanarea network (MAN), or a wide area network (WAN), such as the Internetor the World Wide Web. The networks 104, 104′, 104″ can be a private orpublic network. In one embodiment, network 104′ or network 104″ may be aprivate network and network 104 may be a public network. In someembodiments, network 104 may be a private network and network 104′and/or network 104″ a public network. In another embodiment, networks104, 104′, 104″ may be private networks. In some embodiments, clients102 may be located at a branch office of a corporate enterprisecommunicating via a WAN connection over the network 104 to the servers106 located on a corporate LAN in a corporate data center.

The network 104 may be any type and/or form of network and may includeany of the following: a point to point network, a broadcast network, awide area network, a local area network, a telecommunications network, adata communication network, a computer network, an ATM (AsynchronousTransfer Mode) network, a SONET (Synchronous Optical Network) network, aSDH (Synchronous Digital Hierarchy) network, a wireless network and awireline network. In some embodiments, the network 104 may comprise awireless link, such as an infrared channel or satellite band. Thetopology of the network 104 may be a bus, star, or ring networktopology. The network 104 and network topology may be of any suchnetwork or network topology as known to those ordinarily skilled in theart capable of supporting the operations described herein.

As depicted in FIG. 1A, a first network optimization appliance 200 isshown between networks 104 and 104′ and a second network optimizationappliance 200′ is also between networks 104′ and 104″. In someembodiments, the appliance 200 may be located on network 104. Forexample, a corporate enterprise may deploy an appliance 200 at thebranch office. In other embodiments, the appliance 200 may be located onnetwork 104′. In some embodiments, the appliance 200′ may be located onnetwork 104′ or network 104″. For example, an appliance 200 may belocated at a corporate data center. In one embodiment, the appliance 200and 200′ are on the same network. In another embodiment, the appliance200 and 200′ are on different networks.

In one embodiment, the appliance 200 is a device for accelerating,optimizing or otherwise improving the performance, operation, or qualityof service of any type and form of network traffic. In some embodiments,the appliance 200 is a performance enhancing proxy. In otherembodiments, the appliance 200 is any type and form of WAN optimizationor acceleration device, sometimes also referred to as a WAN optimizationcontroller. In one embodiment, the appliance 200 is any of the productembodiments referred to as WANScaler manufactured by Citrix Systems,Inc. of Ft. Lauderdale, Fla. In other embodiments, the appliance 200includes any of the product embodiments referred to as BIG-IP linkcontroller and WANjet manufactured by F5 Networks, Inc. of Seattle,Wash. In another embodiment, the appliance 200 includes any of the WXand WXC WAN acceleration device platforms manufactured by JuniperNetworks, Inc. of Sunnyvale, Calif. In some embodiments, the appliance200 includes any of the steelhead line of WAN optimization appliancesmanufactured by Riverbed Technology of San Francisco, Calif. In otherembodiments, the appliance 200 includes any of the WAN related devicesmanufactured by Expand Networks Inc. of Roseland, N.J. In oneembodiment, the appliance 200 includes any of the WAN related appliancesmanufactured by Packeteer Inc. of Cupertino, Calif., such as thePacketShaper, iShared, and SkyX product embodiments provided byPacketeer. In yet another embodiment, the appliance 200 includes any WANrelated appliances and/or software manufactured by Cisco Systems, Inc.of San Jose, Calif., such as the Cisco Wide Area Network ApplicationServices software and network modules, and Wide Area Network engineappliances.

In some embodiments, the appliance 200 provides application and dataacceleration services for branch-office or remote offices. In oneembodiment, the appliance 200 includes optimization of Wide Area FileServices (WAFS). In another embodiment, the appliance 200 acceleratesthe delivery of files, such as via the Common Internet File System(CIFS) protocol. In other embodiments, the appliance 200 providescaching in memory and/or storage to accelerate delivery of applicationsand data. In one embodiment, the appliance 205 provides compression ofnetwork traffic at any level of the network stack or at any protocol ornetwork layer. In another embodiment, the appliance 200 providestransport layer protocol optimizations, flow control, performanceenhancements or modifications and/or management to accelerate deliveryof applications and data over a WAN connection. For example, in oneembodiment, the appliance 200 provides Transport Control Protocol (TCP)optimizations. In other embodiments, the appliance 200 providesoptimizations, flow control, performance enhancements or modificationsand/or management for any session or application layer protocol. Furtherdetails of the optimization techniques, operations and architecture ofthe appliance 200 are discussed below in Section B.

Still referring to FIG. 1A, the network environment may includemultiple, logically-grouped servers 106. In these embodiments, thelogical group of servers may be referred to as a server farm 38. In someof these embodiments, the serves 106 may be geographically dispersed. Insome cases, a farm 38 may be administered as a single entity. In otherembodiments, the server farm 38 comprises a plurality of server farms38. In one embodiment, the server farm executes one or more applicationson behalf of one or more clients 102.

The servers 106 within each farm 38 can be heterogeneous. One or more ofthe servers 106 can operate according to one type of operating systemplatform (e.g., WINDOWS NT, manufactured by Microsoft Corp. of Redmond,Wash.), while one or more of the other servers 106 can operate onaccording to another type of operating system platform (e.g., Unix orLinux). The servers 106 of each farm 38 do not need to be physicallyproximate to another server 106 in the same farm 38. Thus, the group ofservers 106 logically grouped as a farm 38 may be interconnected using awide-area network (WAN) connection or metropolitan-area network (MAN)connection. For example, a farm 38 may include servers 106 physicallylocated in different continents or different regions of a continent,country, state, city, campus, or room. Data transmission speeds betweenservers 106 in the farm 38 can be increased if the servers 106 areconnected using a local-area network (LAN) connection or some form ofdirect connection.

Servers 106 may be referred to as a file server, application server, webserver, proxy server, or gateway server. In some embodiments, a server106 may have the capacity to function as either an application server oras a master application server. In one embodiment, a server 106 mayinclude an Active Directory. The clients 102 may also be referred to asclient nodes or endpoints. In some embodiments, a client 102 has thecapacity to function as both a client node seeking access toapplications on a server and as an application server providing accessto hosted applications for other clients 102 a-102 n.

In some embodiments, a client 102 communicates with a server 106. In oneembodiment, the client 102 communicates directly with one of the servers106 in a farm 38. In another embodiment, the client 102 executes aprogram neighborhood application to communicate with a server 106 in afarm 38. In still another embodiment, the server 106 provides thefunctionality of a master node. In some embodiments, the client 102communicates with the server 106 in the farm 38 through a network 104.Over the network 104, the client 102 can, for example, request executionof various applications hosted by the servers 106 a-106 n in the farm 38and receive output of the results of the application execution fordisplay. In some embodiments, only the master node provides thefunctionality required to identify and provide address informationassociated with a server 106′ hosting a requested application.

In one embodiment, the server 106 provides functionality of a webserver. In another embodiment, the server 106 a receives requests fromthe client 102, forwards the requests to a second server 106 b andresponds to the request by the client 102 with a response to the requestfrom the server 106 b. In still another embodiment, the server 106acquires an enumeration of applications available to the client 102 andaddress information associated with a server 106 hosting an applicationidentified by the enumeration of applications. In yet anotherembodiment, the server 106 presents the response to the request to theclient 102 using a web interface. In one embodiment, the client 102communicates directly with the server 106 to access the identifiedapplication. In another embodiment, the client 102 receives applicationoutput data, such as display data, generated by an execution of theidentified application on the server 106.

Deployed With Other Appliances.

Referring now to FIG. 1B, another embodiment of a network environment isdepicted in which the network optimization appliance 200 is deployedwith one or more other appliances 205, 205′ (generally referred to asappliance 205 or second appliance 205) such as a gateway, firewall oracceleration appliance. For example, in one embodiment, the appliance205 is a firewall or security appliance while appliance 205′ is a LANacceleration device. In some embodiments, a client 102 may communicateto a server 106 via one or more of the first appliances 200 and one ormore second appliances 205.

One or more appliances 200 and 205 may be located at any point in thenetwork or network communications path between a client 102 and a server106. In some embodiments, a second appliance 205 may be located on thesame network 104 as the first appliance 200. In other embodiments, thesecond appliance 205 may be located on a different network 104 as thefirst appliance 200. In yet another embodiment, a first appliance 200and second appliance 205 is on the same network, for example network104, while the first appliance 200′ and second appliance 205′ is on thesame network, such as network 104″.

In one embodiment, the second appliance 205 includes any type and formof transport control protocol or transport later terminating device,such as a gateway or firewall device. In one embodiment, the appliance205 terminates the transport control protocol by establishing a firsttransport control protocol connection with the client and a secondtransport control connection with the second appliance or server. Inanother embodiment, the appliance 205 terminates the transport controlprotocol by changing, managing or controlling the behavior of thetransport control protocol connection between the client and the serveror second appliance. For example, the appliance 205 may change, queue,forward or transmit network packets in manner to effectively terminatethe transport control protocol connection or to act or simulate asterminating the connection.

In some embodiments, the second appliance 205 is a performance enhancingproxy. In one embodiment, the appliance 205 provides a virtual privatenetwork (VPN) connection. In some embodiments, the appliance 205provides a Secure Socket Layer VPN (SSL VPN) connection. In otherembodiments, the appliance 205 provides an IPsec (Internet ProtocolSecurity) based VPN connection. In some embodiments, the appliance 205provides any one or more of the following functionality: compression,acceleration, load-balancing, switching/routing, caching, and TransportControl Protocol (TCP) acceleration.

In one embodiment, the appliance 205 is any of the product embodimentsreferred to as Access Gateway, Application Firewall, ApplicationGateway, or NetScaler manufactured by Citrix Systems, Inc. of Ft.Lauderdale, Fla. As such, in some embodiments, the appliance 205includes any logic, functions, rules, or operations to perform servicesor functionality such as SSL VPN connectivity, SSL offloading,switching/load balancing, Domain Name Service resolution, LANacceleration and an application firewall.

In some embodiments, the appliance 205 provides a SSL VPN connectionbetween a client 102 and a server 106. For example, a client 102 on afirst network 104 requests to establish a connection to a server 106 ona second network 104′. In some embodiments, the second network 104″ isnot routable from the first network 104. In other embodiments, theclient 102 is on a public network 104 and the server 106 is on a privatenetwork 104′, such as a corporate network. In one embodiment, a clientagent intercepts communications of the client 102 on the first network104, encrypts the communications, and transmits the communications via afirst transport layer connection to the appliance 205. The appliance 205associates the first transport layer connection on the first network 104to a second transport layer connection to the server 106 on the secondnetwork 104. The appliance 205 receives the intercepted communicationfrom the client agent, decrypts the communications, and transmits thecommunication to the server 106 on the second network 104 via the secondtransport layer connection. The second transport layer connection may bea pooled transport layer connection. In one embodiment, the appliance205 provides an end-to-end secure transport layer connection for theclient 102 between the two networks 104, 104′.

In one embodiments, the appliance 205 hosts an intranet internetprotocol or intranetIP address of the client 102 on the virtual privatenetwork 104. The client 102 has a local network identifier, such as aninternet protocol (IP) address and/or host name on the first network104. When connected to the second network 104′ via the appliance 205,the appliance 205 establishes, assigns or otherwise provides anIntranetIP, which is network identifier, such as IP address and/or hostname, for the client 102 on the second network 104′. The appliance 205listens for and receives on the second or private network 104′ for anycommunications directed towards the client 102 using the client'sestablished IntranetIP. In one embodiment, the appliance 205 acts as oron behalf of the client 102 on the second private network 104.

In some embodiment, the appliance 205 has an encryption engine providinglogic, business rules, functions or operations for handling theprocessing of any security related protocol, such as SSL or TLS, or anyfunction related thereto. For example, the encryption engine encryptsand decrypts network packets, or any portion thereof, communicated viathe appliance 205. The encryption engine may also setup or establish SSLor TLS connections on behalf of the client 102 a-102 n, server 106 a-106n, or appliance 200, 205. As such, the encryption engine providesoffloading and acceleration of SSL processing. In one embodiment, theencryption engine uses a tunneling protocol to provide a virtual privatenetwork between a client 102 a-102 n and a server 106 a-106 n. In someembodiments, the encryption engine uses an encryption processor. Inother embodiments, the encryption engine includes executableinstructions running on an encryption processor.

In some embodiments, the appliance 205 provides one or more of thefollowing acceleration techniques to communications between the client102 and server 106: 1) compression, 2) decompression, 3) TransmissionControl Protocol pooling, 4) Transmission Control Protocol multiplexing,5) Transmission Control Protocol buffering, and 6) caching. In oneembodiment, the appliance 200 relieves servers 106 of much of theprocessing load caused by repeatedly opening and closing transportlayers connections to clients 102 by opening one or more transport layerconnections with each server 106 and maintaining these connections toallow repeated data accesses by clients via the Internet. This techniqueis referred to herein as “connection pooling”.

In some embodiments, in order to seamlessly splice communications from aclient 102 to a server 106 via a pooled transport layer connection, theappliance 205 translates or multiplexes communications by modifyingsequence number and acknowledgment numbers at the transport layerprotocol level. This is referred to as “connection multiplexing”. Insome embodiments, no application layer protocol interaction is required.For example, in the case of an in-bound packet (that is, a packetreceived from a client 102), the source network address of the packet ischanged to that of an output port of appliance 205, and the destinationnetwork address is changed to that of the intended server. In the caseof an outbound packet (that is, one received from a server 106), thesource network address is changed from that of the server 106 to that ofan output port of appliance 205 and the destination address is changedfrom that of appliance 205 to that of the requesting client 102. Thesequence numbers and acknowledgment numbers of the packet are alsotranslated to sequence numbers and acknowledgement expected by theclient 102 on the appliance's 205 transport layer connection to theclient 102. In some embodiments, the packet checksum of the transportlayer protocol is recalculated to account for these translations.

In another embodiment, the appliance 205 provides switching orload-balancing functionality for communications between the client 102and server 106. In some embodiments, the appliance 205 distributestraffic and directs client requests to a server 106 based on layer 4payload or application-layer request data. In one embodiment, althoughthe network layer or layer 2 of the network packet identifies adestination server 106, the appliance 205 determines the server 106 todistribute the network packet by application information and datacarried as payload of the transport layer packet. In one embodiment, ahealth monitoring program of the appliance 205 monitors the health ofservers to determine the server 106 for which to distribute a client'srequest. In some embodiments, if the appliance 205 detects a server 106is not available or has a load over a predetermined threshold, theappliance 205 can direct or distribute client requests to another server106.

In some embodiments, the appliance 205 acts as a Domain Name Service(DNS) resolver or otherwise provides resolution of a DNS request fromclients 102. In some embodiments, the appliance intercepts' a DNSrequest transmitted by the client 102. In one embodiment, the appliance205 responds to a client's DNS request with an IP address of or hostedby the appliance 205. In this embodiment, the client 102 transmitsnetwork communication for the domain name to the appliance 200. Inanother embodiment, the appliance 200 responds to a client's DNS requestwith an IP address of or hosted by a second appliance 200′. In someembodiments, the appliance 205 responds to a client's DNS request withan IP address of a server 106 determined by the appliance 200.

In yet another embodiment, the appliance 205 provides applicationfirewall functionality for communications between the client 102 andserver 106. In one embodiment, a policy engine 295′ provides rules fordetecting and blocking illegitimate requests. In some embodiments, theapplication firewall protects against denial of service (DoS) attacks.In other embodiments, the appliance inspects the content of interceptedrequests to identify and block application-based attacks. In someembodiments, the rules/policy engine includes one or more applicationfirewall or security control policies for providing protections againstvarious classes and types of web or Internet based vulnerabilities, suchas one or more of the following: 1) buffer overflow, 2) CGI-BINparameter manipulation, 3) form/hidden field manipulation, 4) forcefulbrowsing, 5) cookie or session poisoning, 6) broken access control list(ACLs) or weak passwords, 7) cross-site scripting (XSS), 8) commandinjection, 9) SQL injection, 10) error triggering sensitive informationleak, 11) insecure use of cryptography, 12) server misconfiguration, 13)back doors and debug options, 14) website defacement, 15) platform oroperating systems vulnerabilities, and 16) zero-day exploits. In anembodiment, the application firewall of the appliance provides HTML formfield protection in the form of inspecting or analyzing the networkcommunication for one or more of the following: 1) required fields arereturned, 2) no added field allowed, 3) read-only and hidden fieldenforcement, 4) drop-down list and radio button field conformance, and5) form-field max-length enforcement. In some embodiments, theapplication firewall of the appliance 205 ensures cookies are notmodified. In other embodiments, the appliance 205 protects againstforceful browsing by enforcing legal URLs.

In still yet other embodiments, the application firewall appliance 205protects any confidential information contained in the networkcommunication. The appliance 205 may inspect or analyze any networkcommunication in accordance with the rules or polices of the policyengine to identify any confidential information in any field of thenetwork packet. In some embodiments, the application firewall identifiesin the network communication one or more occurrences of a credit cardnumber, password, social security number, name, patient code, contactinformation, and age. The encoded portion of the network communicationmay include these occurrences or the confidential information. Based onthese occurrences, in one embodiment, the application firewall may takea policy action on the network communication, such as preventtransmission of the network communication. In another embodiment, theapplication firewall may rewrite, remove or otherwise mask suchidentified occurrence or confidential information.

Although generally referred to as a network optimization or firstappliance 200 and a second appliance 205, the first appliance 200 andsecond appliance 205 may be the same type and form of appliance. In oneembodiment, the second appliance 205 may perform the same functionality,or portion thereof, as the first appliance 200, and vice-versa. Forexample, the first appliance 200 and second appliance 205 may bothprovide acceleration techniques. In one embodiment, the first appliancemay perform LAN acceleration while the second appliance performs WANacceleration, or vice-versa. In another example, the first appliance 200may also be a transport control protocol terminating device as with thesecond appliance 205. Furthermore, although appliances 200 and 205 areshown as separate devices on the network, the appliance 200 and/or 205could be a part of any client 102 or server 106.

Referring now to FIG. 1C, other embodiments of a network environment fordeploying the appliance 200 are depicted. In another embodiment asdepicted on the top of FIG. 1C, the appliance 200 may be deployed as asingle appliance or single proxy on the network 104. For example, theappliance 200 may be designed, constructed or adapted to perform WANoptimization techniques discussed herein without a second cooperatingappliance 200′. In other embodiments as depicted on the bottom of FIG.1C, a single appliance 200 may be deployed with one or more secondappliances 205. For example, a WAN acceleration first appliance 200,such as a Citrix WANScaler appliance, may be deployed with a LANaccelerating or Application Firewall second appliance 205, such as aCitrix NetScaler appliance.

Computing Device

The client 102, server 106, and appliance 200 and 205 may be deployed asand/or executed on any type and form of computing device, such as acomputer, network device or appliance capable of communicating on anytype and form of network and performing the operations described herein.FIGS. 1C and 1D depict block diagrams of a computing device 100 usefulfor practicing an embodiment of the client 102, server 106 or appliance200. As shown in FIGS. 1C and 1D, each computing device 100 includes acentral processing unit 101, and a main memory unit 122. As shown inFIG. 1C, a computing device 100 may include a visual display device 124,a keyboard 126 and/or a pointing device 127, such as a mouse. Eachcomputing device 100 may also include additional optional elements, suchas one or more input/output devices 130 a-130 b (generally referred tousing reference numeral 130), and a cache memory 140 in communicationwith the central processing unit 101.

The central processing unit 101 is any logic circuitry that responds toand processes instructions fetched from the main memory unit 122. Inmany embodiments, the central processing unit is provided by amicroprocessor unit, such as: those manufactured by Intel Corporation ofMountain View, Calif.; those manufactured by Motorola Corporation ofSchaumburg, Ill.; those manufactured by Transmeta Corporation of SantaClara, Calif.; the RS/6000 processor, those manufactured byInternational Business Machines of White Plains, N.Y.; or thosemanufactured by Advanced Micro Devices of Sunnyvale, Calif. Thecomputing device 100 may be based on any of these processors, or anyother processor capable of operating as described herein.

Main memory unit 122 may be one or more memory chips capable of storingdata and allowing any storage location to be directly accessed by themicroprocessor 101, such as Static random access memory (SRAM), BurstSRAM or SynchBurst SRAM (BSRAM), Dynamic random access memory (DRAM),Fast Page Mode DRAM (FPM DRAM), Enhanced DRAM (EDRAM), Extended DataOutput RAM (EDO RAM), Extended Data Output DRAM (EDO DRAM), BurstExtended Data Output DRAM (BEDO DRAM), Enhanced DRAM (EDRAM),synchronous DRAM (SDRAM), JEDEC SRAM, PC100 SDRAM, Double Data RateSDRAM (DDR SDRAM), Enhanced SDRAM (ESDRAM), SyncLink DRAM (SLDRAM),Direct Rambus DRAM (DRDRAM), or Ferroelectric RAM (FRAM). The mainmemory 122 may be based on any of the above described memory chips, orany other available memory chips capable of operating as describedherein. In the embodiment shown in FIG. 1C, the processor 101communicates with main memory 122 via a system bus 150 (described inmore detail below). FIG. 1C depicts an embodiment of a computing device100 in which the processor communicates directly with main memory 122via a memory port 103. For example, in FIG. 1D the main memory 122 maybe DRDRAM.

FIG. 1D depicts an embodiment in which the main processor 101communicates directly with cache memory 140 via a secondary bus,sometimes referred to as a backside bus. In other embodiments, the mainprocessor 101 communicates with cache memory 140 using the system bus150. Cache memory 140 typically has a faster response time than mainmemory 122 and is typically provided by SRAM, BSRAM, or EDRAM. In theembodiment shown in FIG. 1C, the processor 101 communicates with variousI/O devices 130 via a local system bus 150. Various busses may be usedto connect the central processing unit 101 to any of the I/O devices130, including a VESA VL bus, an ISA bus, an EISA bus, a MicroChannelArchitecture (MCA) bus, a PCI bus, a PCI-X bus, a PCI-Express bus, or aNuBus. For embodiments in which the I/O device is a video display 124,the processor 101 may use an Advanced Graphics Port (AGP) to communicatewith the display 124. FIG. 1D depicts an embodiment of a computer 100 inwhich the main processor 101 communicates directly with I/O device 130via HyperTransport, Rapid I/O, or InfiniBand. FIG. 1D also depicts anembodiment in which local busses and direct communication are mixed: theprocessor 101 communicates with I/O device 130 using a localinterconnect bus while communicating with I/O device 130 directly.

The computing device 100 may support any suitable installation device116, such as a floppy disk drive for receiving floppy disks such as3.5-inch, 5.25-inch disks or ZIP disks, a CD-ROM drive, a CD-R/RW drive,a DVD-ROM drive, tape drives of various formats, USB device, hard-driveor any other device suitable for installing software and programs suchas any client agent 120, or portion thereof. The computing device 100may further comprise a storage device 128, such as one or more hard diskdrives or redundant arrays of independent disks, for storing anoperating system and other related software, and for storing applicationsoftware programs such as any program related to the client agent 120.Optionally, any of the installation devices 116 could also be used asthe storage device 128. Additionally, the operating system and thesoftware can be run from a bootable medium, for example, a bootable CD,such as KNOPPIX®, a bootable CD for GNU/Linux that is available as aGNU/Linux distribution from knoppix.net.

Furthermore, the computing device 100 may include a network interface118 to interface to a Local Area Network (LAN), Wide Area Network (WAN)or the Internet through a variety of connections including, but notlimited to, standard telephone lines, LAN or WAN links (e.g., 802.11,T1, T3, 56 kb, X.25), broadband connections (e.g., ISDN, Frame Relay,ATM), wireless connections, or some combination of any or all of theabove. The network interface 118 may comprise a built-in networkadapter, network interface card, PCMCIA network card, card bus networkadapter, wireless network adapter, USB network adapter, modem or anyother device suitable for interfacing the computing device 100 to anytype of network capable of communication and performing the operationsdescribed herein.

A wide variety of I/O devices 130 a-130 n may be present in thecomputing device 100.

Input devices include keyboards, mice, trackpads, trackballs,microphones, and drawing tablets. Output devices include video displays,speakers, inkjet printers, laser printers, and dye-sublimation printers.The I/O devices 130 may be controlled by an I/O controller 123 as shownin FIG. 1C. The I/O controller may control one or more I/O devices suchas a keyboard 126 and a pointing device 127, e.g., a mouse or opticalpen. Furthermore, an I/O device may also provide storage 128 and/or aninstallation medium 116 for the computing device 100. In still otherembodiments, the computing device 100 may provide USB connections toreceive handheld USB storage devices such as the USB Flash Drive line ofdevices manufactured by Twintech Industry, Inc. of Los Alamitos, Calif.

In some embodiments, the computing device 100 may comprise or beconnected to multiple display devices 124 a-124 n, which each may be ofthe same or different type and/or form. As such, any of the I/O devices130 a-130 n and/or the I/O controller 123 may comprise any type and/orform of suitable hardware, software, or combination of hardware andsoftware to support, enable or provide for the connection and use ofmultiple display devices 124 a-124 n by the computing device 100. Forexample, the computing device 100 may include any type and/or form ofvideo adapter, video card, driver, and/or library to interface,communicate, connect or otherwise use the display devices 124 a-124 n.In one embodiment, a video adapter may comprise multiple connectors tointerface to multiple display devices 124 a-124 n. In other embodiments,the computing device 100 may include multiple video adapters, with eachvideo adapter connected to one or more of the display devices 124 a-124n. In some embodiments, any portion of the operating system of thecomputing device 100 may be configured for using multiple displays 124a-124 n. In other embodiments, one or more of the display devices 124a-124 n may be provided by one or more other computing devices, such ascomputing devices 100 a and 100 b connected to the computing device 100,for example, via a network. These embodiments may include any type ofsoftware designed and constructed to use another computer's displaydevice as a second display device 124 a for the computing device 100.One ordinarily skilled in the art will recognize and appreciate thevarious ways and embodiments that a computing device 100 may beconfigured to have multiple display devices 124 a-124 n.

In further embodiments, an I/O device 130 may be a bridge 170 betweenthe system bus 150 and an external communication bus, such as a USB bus,an Apple Desktop Bus, an RS-232 serial connection, a SCSI bus, aFireWire bus, a FireWire 800 bus, an Ethernet bus, an AppleTalk bus, aGigabit Ethernet bus, an Asynchronous Transfer Mode bus, a HIPPI bus, aSuper HIPPI bus, a SerialPlus bus, a SCI/LAMP bus, a FibreChannel bus,or a Serial Attached small computer system interface bus.

A computing device 100 of the sort depicted in FIGS. 1C and 1D typicallyoperate under the control of operating systems, which control schedulingof tasks and access to system resources. The computing device 100 can berunning any operating system such as any of the versions of theMicrosoft® Windows operating systems, the different releases of the Unixand Linux operating systems, any version of the Mac OS® for Macintoshcomputers, any embedded operating system, any real-time operatingsystem, any open source operating system, any proprietary operatingsystem, any operating systems for mobile computing devices, or any otheroperating system capable of running on the computing device andperforming the operations described herein. Typical operating systemsinclude: WINDOWS 3.x, WINDOWS 95, WINDOWS 98, WINDOWS 2000, WINDOWS NT3.51, WINDOWS NT 4.0, WINDOWS CE, and WINDOWS XP, all of which aremanufactured by Microsoft Corporation of Redmond, Wash.; MacOS,manufactured by Apple Computer of Cupertino, Calif.; OS/2, manufacturedby International Business Machines of Armonk, N.Y.; and Linux, afreely-available operating system distributed by Caldera Corp. of SaltLake City, Utah, or any type and/or form of a Unix operating system,among others.

In other embodiments, the computing device 100 may have differentprocessors, operating systems, and input devices consistent with thedevice. For example, in one embodiment the computer 100 is a Treo 180,270, 1060, 600 or 650 smart phone manufactured by Palm, Inc. In thisembodiment, the Treo smart phone is operated under the control of thePalmOS operating system and includes a stylus input device as well as afive-way navigator device. Moreover, the computing device 100 can be anyworkstation, desktop computer, laptop or notebook computer, server,handheld computer, mobile telephone, any other computer, or other formof computing or telecommunications device that is capable ofcommunication and that has sufficient processor power and memorycapacity to perform the operations described herein.

B. System and Appliance Architecture

Referring now to FIG. 2A, an embodiment of a system environment andarchitecture of an appliance 200 for delivering and/or operating acomputing environment on a client is depicted. In some embodiments, aserver 106 includes an application delivery system 290 for delivering acomputing environment or an application and/or data file to one or moreclients 102. In brief overview, a client 102 is in communication with aserver 106 via network 104 and appliance 200. For example, the client102 may reside in a remote office of a company, e.g., a branch office,and the server 106 may reside at a corporate data center. The client 102has a client agent 120, and a computing environment 215. The computingenvironment 215 may execute or operate an application that accesses,processes or uses a data file. The computing environment 215,application and/or data file may be delivered via the appliance 200and/or the server 106.

In some embodiments, the appliance 200 accelerates delivery of acomputing environment 215, or any portion thereof, to a client 102. Inone embodiment, the appliance 200 accelerates the delivery of thecomputing environment 215 by the application delivery system 290. Forexample, the embodiments described herein may be used to acceleratedelivery of a streaming application and data file processable by theapplication from a central corporate data center to a remote userlocation, such as a branch office of the company. In another embodiment,the appliance 200 accelerates transport layer traffic between a client102 and a server 106. In another embodiment, the appliance 200 controls,manages, or adjusts the transport layer protocol to accelerate deliveryof the computing environment. In some embodiments, the appliance 200uses caching and/or compression techniques to accelerate delivery of acomputing environment.

In some embodiments, the application delivery management system 290provides application delivery techniques to deliver a computingenvironment to a desktop of a user, remote or otherwise, based on aplurality of execution methods and based on any authentication andauthorization policies applied via a policy engine 295. With thesetechniques, a remote user may obtain a computing environment and accessto server stored applications and data files from any network connecteddevice 100. In one embodiment, the application delivery system 290 mayreside or execute on a server 106. In another embodiment, theapplication delivery system 290 may reside or execute on a plurality ofservers 106 a-106 n. In some embodiments, the application deliverysystem 290 may execute in a server farm 38. In one embodiment, theserver 106 executing the application delivery system 290 may also storeor provide the application and data file. In another embodiment, a firstset of one or more servers 106 may execute the application deliverysystem 290, and a different server 106 n may store or provide theapplication and data file. In some embodiments, each of the applicationdelivery system 290, the application, and data file may reside or belocated on different servers. In yet another embodiment, any portion ofthe application delivery system 290 may reside, execute or be stored onor distributed to the appliance 200, or a plurality of appliances.

The client 102 may include a computing environment 215 for executing anapplication that uses or processes a data file. The client 102 vianetworks 104, 104′ and appliance 200 may request an application and datafile from the server 106. In one embodiment, the appliance 200 mayforward a request from the client 102 to the server 106. For example,the client 102 may not have the application and data file stored oraccessible locally. In response to the request, the application deliverysystem 290 and/or server 106 may deliver the application and data fileto the client 102. For example, in one embodiment, the server 106 maytransmit the application as an application stream to operate incomputing environment 215 on client 102.

In some embodiments, the application delivery system 290 comprises anyportion of the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™ and/or any of the Microsoft®Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application delivery system 290 may deliver one ormore applications to clients 102 or users via a remote-display protocolor otherwise via remote-based or server-based computing. In anotherembodiment, the application delivery system 290 may deliver one or moreapplications to clients or users via steaming of the application.

In one embodiment, the application delivery system 290 includes a policyengine 295 for controlling and managing the access to, selection ofapplication execution methods and the delivery of applications. In someembodiments, the policy engine 295 determines the one or moreapplications a user or client 102 may access. In another embodiment, thepolicy engine 295 determines how the application should be delivered tothe user or client 102, e.g., the method of execution. In someembodiments, the application delivery system 290 provides a plurality ofdelivery techniques from which to select a method of applicationexecution, such as a server-based computing, streaming or delivering theapplication locally to the client 120 for local execution.

In one embodiment, a client 102 requests execution of an applicationprogram and the application delivery system 290 comprising a server 106selects a method of executing the application program. In someembodiments, the server 106 receives credentials from the client 102. Inanother embodiment, the server 106 receives a request for an enumerationof available applications from the client 102. In one embodiment, inresponse to the request or receipt of credentials, the applicationdelivery system 290 enumerates a plurality of application programsavailable to the client 102. The application delivery system 290receives a request to execute an enumerated application. The applicationdelivery system 290 selects one of a predetermined number of methods forexecuting the enumerated application, for example, responsive to apolicy of a policy engine. The application delivery system 290 mayselect a method of execution of the application enabling the client 102to receive application-output data generated by execution of theapplication program on a server 106. The application delivery system 290may select a method of execution of the application enabling the clientor local machine 102 to execute the application program locally afterretrieving a plurality of application files comprising the application.In yet another embodiment, the application delivery system 290 mayselect a method of execution of the application to stream theapplication via the network 104 to the client 102.

A client 102 may execute, operate or otherwise provide an application,which can be any type and/or form of software, program, or executableinstructions such as any type and/or form of web browser, web-basedclient, client-server application, a thin-client computing client, anActiveX control, or a Java applet, or any other type and/or form ofexecutable instructions capable of executing on client 102. In someembodiments, the application may be a server-based or a remote-basedapplication executed on behalf of the client 102 on a server 106. In oneembodiment the server 106 may display output to the client 102 using anythin-client or remote-display protocol, such as the IndependentComputing Architecture (ICA) protocol manufactured by Citrix Systems,Inc. of Ft. Lauderdale, Fla. or the Remote Desktop Protocol (RDP)manufactured by the Microsoft Corporation of Redmond, Wash. Theapplication can use any type of protocol and it can be, for example, anHTTP client, an FTP client, an Oscar client, or a Telnet client. Inother embodiments, the application comprises any type of softwarerelated to VoIP communications, such as a soft IP telephone. In furtherembodiments, the application comprises any application related toreal-time data communications, such as applications for streaming videoand/or audio.

In some embodiments, the server 106 or a server farm 38 may be runningone or more applications, such as an application providing a thin-clientcomputing or remote display presentation application. In one embodiment,the server 106 or server farm 38 executes as an application, any portionof the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™, and/or any of the Microsoft®Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application is an ICA client, developed by CitrixSystems, Inc. of Fort Lauderdale, Fla. In other embodiments, theapplication includes a Remote Desktop (RDP) client, developed byMicrosoft Corporation of Redmond, Wash. Also, the server 106 may run anapplication, which for example, may be an application server providingemail services such as Microsoft Exchange manufactured by the MicrosoftCorporation of Redmond, Wash., a web or Internet server, or a desktopsharing server, or a collaboration server. In some embodiments, any ofthe applications may comprise any type of hosted service or products,such as GoToMeeting™ provided by Citrix Online Division, Inc. of SantaBarbara, Calif., WebEx™ provided by WebEx, Inc. of Santa Clara, Calif.,or Microsoft Office Live Meeting provided by Microsoft Corporation ofRedmond, Wash.

Example Appliance Architecture

FIG. 2A also illustrates an example embodiment of the appliance 200. Thearchitecture of the appliance 200 in FIG. 2A is provided by way ofillustration only and is not intended to be limiting in any manner. Theappliance 200 may include any type and form of computing device 100,such as any element or portion described in conjunction with FIGS. 1Dand 1E above. In brief overview, the appliance 200 has one or morenetwork ports 266A-226N and one or more networks stacks 267A-267N forreceiving and/or transmitting communications via networks 104. Theappliance 200 also has a network optimization engine 250 for optimizing,accelerating or otherwise improving the performance, operation, orquality of any network traffic or communications traversing theappliance 200.

The appliance 200 includes or is under the control of an operatingsystem. The operating system of the appliance 200 may be any type and/orform of Unix operating system although the invention is not so limited.As such, the appliance 200 can be running any operating system such asany of the versions of the Microsoft® Windows operating systems, thedifferent releases of the Unix and Linux operating systems, any versionof the Mac OS® for Macintosh computers, any embedded operating system,any network operating system, any real-time operating system, any opensource operating system, any proprietary operating system, any operatingsystems for mobile computing devices or network devices, or any otheroperating system capable of running on the appliance 200 and performingthe operations described herein.

The operating system of appliance 200 allocates, manages, or otherwisesegregates the available system memory into what is referred to askernel or system space, and user or application space. The kernel spaceis typically reserved for running the kernel, including any devicedrivers, kernel extensions or other kernel related software. As known tothose skilled in the art, the kernel is the core of the operatingsystem, and provides access, control, and management of resources andhardware-related elements of the appliance 200. In accordance with anembodiment of the appliance 200, the kernel space also includes a numberof network services or processes working in conjunction with the networkoptimization engine 250, or any portion thereof. Additionally, theembodiment of the kernel will depend on the embodiment of the operatingsystem installed, configured, or otherwise used by the device 200. Incontrast to kernel space, user space is the memory area or portion ofthe operating system used by user mode applications or programsotherwise running in user mode. A user mode application may not accesskernel space directly and uses service calls in order to access kernelservices. The operating system uses the user or application space forexecuting or running applications and provisioning of user levelprograms, services, processes and/or tasks.

The appliance 200 has one or more network ports 266 for transmitting andreceiving data over a network 104. The network port 266 provides aphysical and/or logical interface between the computing device and anetwork 104 or another device 100 for transmitting and receiving networkcommunications. The type and form of network port 266 depends on thetype and form of network and type of medium for connecting to thenetwork. Furthermore, any software of, provisioned for or used by thenetwork port 266 and network stack 267 may run in either kernel space oruser space.

In one embodiment, the appliance 200 has one network stack 267, such asa TCP/IP based stack, for communicating on a network 105, such with theclient 102 and/or the server 106. In one embodiment, the network stack267 is used to communicate with a first network, such as network 104,and also with a second network 104′. In another embodiment, theappliance 200 has two or more network stacks, such as first networkstack 267A and a second network stack 267N. The first network stack 267Amay be used in conjunction with a first port 266A to communicate on afirst network 104. The second network stack 267N may be used inconjunction with a second port 266N to communicate on a second network104′. In one embodiment, the network stack(s) 267 has one or morebuffers for queuing one or more network packets for transmission by theappliance 200.

The network stack 267 includes any type and form of software, orhardware, or any combinations thereof, for providing connectivity to andcommunications with a network. In one embodiment, the network stack 267includes a software implementation for a network protocol suite. Thenetwork stack 267 may have one or more network layers, such as anynetworks layers of the Open Systems Interconnection (OSI) communicationsmodel as those skilled in the art recognize and appreciate. As such, thenetwork stack 267 may have any type and form of protocols for any of thefollowing layers of the OSI model: 1) physical link layer, 2) data linklayer, 3) network layer, 4) transport layer, 5) session layer, 6)presentation layer, and 7) application layer. In one embodiment, thenetwork stack 267 includes a transport control protocol (TCP) over thenetwork layer protocol of the internet protocol (IP), generally referredto as TCP/IP. In some embodiments, the TCP/IP protocol may be carriedover the Ethernet protocol, which may comprise any of the family of IEEEwide-area-network (WAN) or local-area-network (LAN) protocols, such asthose protocols covered by the IEEE 802.3. In some embodiments, thenetwork stack 267 has any type and form of a wireless protocol, such asIEEE 802.11 and/or mobile internet protocol.

In view of a TCP/IP based network, any TCP/IP based protocol may beused, including Messaging Application Programming Interface (MAPI)(email), File Transfer Protocol (FTP), HyperText Transfer Protocol(HTTP), Common Internet File System (CIFS) protocol (file transfer),Independent Computing Architecture (ICA) protocol, Remote DesktopProtocol (RDP), Wireless Application Protocol (WAP), Mobile IP protocol,and Voice Over IP (VoIP) protocol. In another embodiment, the networkstack 267 comprises any type and form of transport control protocol,such as a modified transport control protocol, for example a TransactionTCP (T/TCP), TCP with selection acknowledgements (TCP-SACK), TCP withlarge windows (TCP-LW), a congestion prediction protocol such as theTCP-Vegas protocol, and a TCP spoofing protocol. In other embodiments,any type and form of user datagram protocol (UDP), such as UDP over IP,may be used by the network stack 267, such as for voice communicationsor real-time data communications.

Furthermore, the network stack 267 may include one or more networkdrivers supporting the one or more layers, such as a TCP driver or anetwork layer driver. The network drivers may be included as part of theoperating system of the computing device 100 or as part of any networkinterface cards or other network access components of the computingdevice 100. In some embodiments, any of the network drivers of thenetwork stack 267 may be customized, modified or adapted to provide acustom or modified portion of the network stack 267 in support of any ofthe techniques described herein.

In one embodiment, the appliance 200 provides for or maintains atransport layer connection between a client 102 and server 106 using asingle network stack 267. In some embodiments, the appliance 200effectively terminates the transport layer connection by changing,managing or controlling the behavior of the transport control protocolconnection between the client and the server. In these embodiments, theappliance 200 may use a single network stack 267. In other embodiments,the appliance 200 terminates a first transport layer connection, such asa TCP connection of a client 102, and establishes a second transportlayer connection to a server 106 for use by or on behalf of the client102, e.g., the second transport layer connection is terminated at theappliance 200 and the server 106. The first and second transport layerconnections may be established via a single network stack 267. In otherembodiments, the appliance 200 may use multiple network stacks, forexample 267A and 267N. In these embodiments, the first transport layerconnection may be established or terminated at one network stack 267A,and the second transport layer connection may be established orterminated on the second network stack 267N. For example, one networkstack may be for receiving and transmitting network packets on a firstnetwork, and another network stack for receiving and transmittingnetwork packets on a second network.

As shown in FIG. 2A, the network optimization engine 250 includes one ormore of the following elements, components or modules: network packetprocessing engine 240, LAN/WAN detector 210, flow controller 220, QoSengine 236, protocol accelerator 234, compression engine 238, cachemanager 232 and policy engine 295′. The network optimization engine 250,or any portion thereof, may include software, hardware or anycombination of software and hardware. Furthermore, any software of,provisioned for or used by the network optimization engine 250 may runin either kernel space or user space. For example, in one embodiment,the network optimization engine 250 may run in kernel space. In anotherembodiment, the network optimization engine 250 may run in user space.In yet another embodiment, a first portion of the network optimizationengine 250 runs in kernel space while a second portion of the networkoptimization engine 250 runs in user space.

Network Packet Processing Engine

The network packet engine 240, also generally referred to as a packetprocessing engine or packet engine, is responsible for controlling andmanaging the processing of packets received and transmitted by appliance200 via network ports 266 and network stack(s) 267. The network packetengine 240 may operate at any layer of the network stack 267. In oneembodiment, the network packet engine 240 operates at layer 2 or layer 3of the network stack 267. In some embodiments, the packet engine 240intercepts or otherwise receives packets at the network layer, such asthe IP layer in a TCP/IP embodiment. In another embodiment, the packetengine 240 operates at layer 4 of the network stack 267. For example, insome embodiments, the packet engine 240 intercepts or otherwise receivespackets at the transport layer, such as intercepting packets as the TCPlayer in a TCP/IP embodiment. In other embodiments, the packet engine240 operates at any session or application layer above layer 4. Forexample, in one embodiment, the packet engine 240 intercepts orotherwise receives network packets above the transport layer protocollayer, such as the payload of a TCP packet in a TCP embodiment.

The packet engine 240 may include a buffer for queuing one or morenetwork packets during processing, such as for receipt of a networkpacket or transmission of a network packet. Additionally, the packetengine 240 is in communication with one or more network stacks 267 tosend and receive network packets via network ports 266. The packetengine 240 may include a packet processing timer. In one embodiment, thepacket processing timer provides one or more time intervals to triggerthe processing of incoming, i.e., received, or outgoing, i.e.,transmitted, network packets. In some embodiments, the packet engine 240processes network packets responsive to the timer. The packet processingtimer provides any type and form of signal to the packet engine 240 tonotify, trigger, or communicate a time related event, interval oroccurrence. In many embodiments, the packet processing timer operates inthe order of milliseconds, such as for example 100 ms, 50 ms, 25 ms, 10ms, 5 ms or 1 ms.

During operations, the packet engine 240 may be interfaced, integratedor be in communication with any portion of the network optimizationengine 250, such as the LAN/WAN detector 210, flow controller 220, QoSengine 236, protocol accelerator 234, compression engine 238, cachemanager 232 and/or policy engine 295′. As such, any of the logic,functions, or operations of the LAN/WAN detector 210, flow controller220, QoS engine 236, protocol accelerator 234, compression engine 238,cache manager 232 and policy engine 295′ may be performed responsive tothe packet processing timer and/or the packet engine 240. In someembodiments, any of the logic, functions, or operations of theencryption engine 234, cache manager 232, policy engine 236 andmulti-protocol compression logic 238 may be performed at the granularityof time intervals provided via the packet processing timer, for example,at a time interval of less than or equal to 10 ms. For example, in oneembodiment, the cache manager 232 may perform expiration of any cachedobjects responsive to the integrated packet engine 240 and/or the packetprocessing timer 242. In another embodiment, the expiry or invalidationtime of a cached object can be set to the same order of granularity asthe time interval of the packet processing timer, such as at every 10ms.

Cache Manager

The cache manager 232 may include software, hardware or any combinationof software and hardware to store data, information and objects to acache in memory or storage, provide cache access, and control and managethe cache. The data, objects or content processed and stored by thecache manager 232 may include data in any format, such as a markuplanguage, or any type of data communicated via any protocol. In someembodiments, the cache manager 232 duplicates original data storedelsewhere or data previously computed, generated or transmitted, inwhich the original data may require longer access time to fetch, computeor otherwise obtain relative to reading a cache memory or storageelement. Once the data is stored in the cache, future use can be made byaccessing the cached copy rather than refetching or recomputing theoriginal data, thereby reducing the access time. In some embodiments,the cache may comprise a data object in memory of the appliance 200. Inanother embodiment, the cache may comprise any type and form of storageelement of the appliance 200, such as a portion of a hard disk. In someembodiments, the processing unit of the device may provide cache memoryfor use by the cache manager 232. In yet further embodiments, the cachemanager 232 may use any portion and combination of memory, storage, orthe processing unit for caching data, objects, and other content.

Furthermore, the cache manager 232 includes any logic, functions, rules,or operations to perform any caching techniques of the appliance 200. Insome embodiments, the cache manager 232 may operate as an application,library, program, service, process, thread or task. In some embodiments,the cache manager 232 can comprise any type of general purpose processor(GPP), or any other type of integrated circuit, such as a FieldProgrammable Gate Array (FPGA), Programmable Logic Device (PLD), orApplication Specific Integrated Circuit (ASIC).

Policy Engine

The policy engine 295′ includes any logic, function or operations forproviding and applying one or more policies or rules to the function,operation or configuration of any portion of the appliance 200. Thepolicy engine 295′ may include, for example, an intelligent statisticalengine or other programmable application(s). In one embodiment, thepolicy engine 295 provides a configuration mechanism to allow a user toidentify, specify, define or configure a policy for the networkoptimization engine 250, or any portion thereof. For example, the policyengine 295 may provide policies for what data to cache, when to cachethe data, for whom to cache the data, when to expire an object in cacheor refresh the cache. In other embodiments, the policy engine 236 mayinclude any logic, rules, functions or operations to determine andprovide access, control and management of objects, data or content beingcached by the appliance 200 in addition to access, control andmanagement of security, network traffic, network access, compression orany other function or operation performed by the appliance 200.

In some embodiments, the policy engine 295′ provides and applies one ormore policies based on any one or more of the following: a user,identification of the client, identification of the server, the type ofconnection, the time of the connection, the type of network, or thecontents of the network traffic. In one embodiment, the policy engine295′ provides and applies a policy based on any field or header at anyprotocol layer of a network packet. In another embodiment, the policyengine 295′ provides and applies a policy based on any payload of anetwork packet. For example, in one embodiment, the policy engine 295′applies a policy based on identifying a certain portion of content of anapplication layer protocol carried as a payload of a transport layerpacket. In another example, the policy engine 295′ applies a policybased on any information identified by a client, server or usercertificate. In yet another embodiment, the policy engine 295′ applies apolicy based on any attributes or characteristics obtained about aclient 102, such as via any type and form of endpoint detection (see forexample the collection agent of the client agent discussed below).

In one embodiment, the policy engine 295′ works in conjunction orcooperation with the policy engine 295 of the application deliverysystem 290. In some embodiments, the policy engine 295′ is a distributedportion of the policy engine 295 of the application delivery system 290.In another embodiment, the policy engine 295 of the application deliverysystem 290 is deployed on or executed on the appliance 200. In someembodiments, the policy engines 295, 295′ both operate on the appliance200. In yet another embodiment, the policy engine 295′, or a portionthereof, of the appliance 200 operates on a server 106.

Multi-Protocol and Multi-Layer Compression Engine

The compression engine 238 includes any logic, business rules, functionor operations for compressing one or more protocols of a network packet,such as any of the protocols used by the network stack 267 of theappliance 200. The compression engine 238 may also be referred to as amulti-protocol compression engine 238 in that it may be designed,constructed or capable of compressing a plurality of protocols. In oneembodiment, the compression engine 238 applies context insensitivecompression, which is compression applied to data without knowledge ofthe type of data. In another embodiment, the compression engine 238applies context-sensitive compression. In this embodiment, thecompression engine 238 utilizes knowledge of the data type to select aspecific compression algorithm from a suite of suitable algorithms. Insome embodiments, knowledge of the specific protocol is used to performcontext-sensitive compression. In one embodiment, the appliance 200 orcompression engine 238 can use port numbers (e.g., well-known ports), aswell as data from the connection itself to determine the appropriatecompression algorithm to use. Some protocols use only a single type ofdata, requiring only a single compression algorithm that can be selectedwhen the connection is established. Other protocols contain differenttypes of data at different times. For example, POP, IMAP, SMTP, and HTTPall move files of arbitrary types interspersed with other protocol data.

In one embodiment, the compression engine 238 uses a delta-typecompression algorithm. In another embodiment, the compression engine 238uses first site compression as well as searching for repeated patternsamong data stored in cache, memory or disk. In some embodiments, thecompression engine 238 uses a lossless compression algorithm. In otherembodiments, the compression engine uses a lossy compression algorithm.In some cases, knowledge of the data type and, sometimes, permissionfrom the user are required to use a lossy compression algorithm.Compression is not limited to the protocol payload. The control fieldsof the protocol itself may be compressed. In some embodiments, thecompression engine 238 uses a different algorithm than that used for thepayload.

In some embodiments, the compression engine 238 compresses at one ormore layers of the network stack 267. In one embodiment, the compressionengine 238 compresses at a transport layer protocol. In anotherembodiment, the compression engine 238 compresses at an applicationlayer protocol. In some embodiments, the compression engine 238compresses at a layer 2-4 protocol. In other embodiments, thecompression engine 238 compresses at a layer 5-7 protocol. In yetanother embodiment, the compression engine compresses a transport layerprotocol and an application layer protocol. In some embodiments, thecompression engine 238 compresses a layer 2-4 protocol and a layer 5-7protocol.

In some embodiments, the compression engine 238 uses memory-basedcompression, cache-based compression or disk-based compression or anycombination thereof. As such, the compression engine 238 may be referredto as a multi-layer compression engine. In one embodiment, thecompression engine 238 uses a history of data stored in memory, such asRAM. In another embodiment, the compression engine 238 uses a history ofdata stored in a cache, such as L2 cache of the processor. In otherembodiments, the compression engine 238 uses a history of data stored toa disk or storage location. In some embodiments, the compression engine238 uses a hierarchy of cache-based, memory-based and disk-based datahistory. The compression engine 238 may first use the cache-based datato determine one or more data matches for compression, and then maycheck the memory-based data to determine one or more data matches forcompression. In another case, the compression engine 238 may check diskstorage for data matches for compression after checking either thecache-based and/or memory-based data history.

In one embodiment, multi-protocol compression engine 238 compressesbi-directionally between clients 102 a-102 n and servers 106 a-106 n anyTCP/IP based protocol, including Messaging Application ProgrammingInterface (MAPI) (email), File Transfer Protocol (FTP), HyperTextTransfer Protocol (HTTP), Common Internet File System (CIFS) protocol(file transfer), Independent Computing Architecture (ICA) protocol,Remote Desktop Protocol (RDP), Wireless Application Protocol (WAP),Mobile IP protocol, and Voice Over IP (VoIP) protocol. In otherembodiments, multi-protocol compression engine 238 provides compressionof HyperText Markup Language (HTML) based protocols and in someembodiments, provides compression of any markup languages, such as theExtensible Markup Language (XML). In one embodiment, the multi-protocolcompression engine 238 provides compression of any high-performanceprotocol, such as any protocol designed for appliance 200 to appliance200 communications. In another embodiment, the multi-protocolcompression engine 238 compresses any payload of or any communicationusing a modified transport control protocol, such as Transaction TCP(T/TCP), TCP with selection acknowledgements (TCP-SACK), TCP with largewindows (TCP-LW), a congestion prediction protocol such as the TCP-Vegasprotocol, and a TCP spoofing protocol.

As such, the multi-protocol compression engine 238 acceleratesperformance for users accessing applications via desktop clients, e.g.,Microsoft Outlook and non-Web thin clients, such as any client launchedby popular enterprise applications like Oracle, SAP and Siebel, and evenmobile clients, such as the Pocket PC. In some embodiments, themulti-protocol compression engine by integrating with packet processingengine 240 accessing the network stack 267 is able to compress any ofthe protocols carried by a transport layer protocol, such as anyapplication layer protocol.

LAN/WAN Detector

The LAN/WAN detector 238 includes any logic, business rules, function oroperations for automatically detecting a slow side connection (e.g., awide area network (WAN) connection such as an Intranet) and associatedport 267, and a fast side connection (e.g., a local area network (LAN)connection) and an associated port 267. In some embodiments, the LAN/WANdetector 238 monitors network traffic on the network ports 267 of theappliance 200 to detect a synchronization packet, sometimes referred toas a “tagged” network packet. The synchronization packet identifies atype or speed of the network traffic. In one embodiment, thesynchronization packet identifies a WAN speed or WAN type connection.The LAN/WAN detector 238 also identifies receipt of an acknowledgementpacket to a tagged synchronization packet and on which port it isreceived. The appliance 200 then configures itself to operate theidentified port on which the tagged synchronization packet arrived sothat the speed on that port is set to be the speed associated with thenetwork connected to that port. The other port is then set to the speedassociated with the network connected to that port.

For ease of discussion herein, reference to “fast” side will be madewith respect to connection with a wide area network (WAN), e.g., theInternet, and operating at a network speed of the WAN. Likewise,reference to “slow” side will be made with respect to connection with alocal area network (LAN) and operating at a network speed the LAN.However, it is noted that “fast” and “slow” sides in a network canchange on a per-connection basis and are relative terms to the speed ofthe network connections or to the type of network topology. Suchconfigurations are useful in complex network topologies, where a networkis “fast” or “slow” only when compared to adjacent networks and not inany absolute sense.

In one embodiment, the LAN/WAN detector 238 may be used to allow forauto-discovery by an appliance 200 of a network to which it connects. Inanother embodiment, the LAN/WAN detector 238 may be used to detect theexistence or presence of a second appliance 200′ deployed in the network104. For example, an auto-discovery mechanism in operation in accordancewith FIG. 1A functions as follows: appliance 200 and 200′ are placed inline with the connection linking client 102 and server 106. Theappliances 200 and 200′ are at the ends of a low-speed link, e.g.,Internet, connecting two LANs. In one example embodiment, appliances 200and 200′ each include two ports—one to connect with the “lower” speedlink and the other to connect with a “higher” speed link, e.g., a LAN.Any packet arriving at one port is copied to the other port. Thus,appliance 200 and 200′ are each configured to function as a bridgebetween the two networks 104.

When an end node, such as the client 102, opens a new TCP connectionwith another end node, such as the server 106, the client 102 sends aTCP packet with a synchronization (SYN) header bit set, or a SYN packet,to the server 106. In the present example, client 102 opens a transportlayer connection to server 106. When the SYN packet passes throughappliance 200, the appliance 200 inserts, attaches or otherwise providesa characteristic TCP header option to the packet, which announces itspresence. If the packet passes through a second appliance, in thisexample appliance 200′ the second appliance notes the header option onthe SYN packet. The server 106 responds to the SYN packet with asynchronization acknowledgment (SYN-ACK) packet. When the SYN-ACK packetpasses through appliance 200′, a TCP header option is tagged (e.g.,attached, inserted or added) to the SYN-ACK packet to announce appliance200′ presence to appliance 200. When appliance 200 receives this packet,both appliances 200, 200′ are now aware of each other and the connectioncan be appropriately accelerated.

Further to the operations of the LAN/WAN detector 238, a method orprocess for detecting “fast” and “slow” sides of a network using a SYNpacket is described. During a transport layer connection establishmentbetween a client 102 and a server 106, the appliance 200 via the LAN/WANdetector 238 determines whether the SYN packet is tagged with anacknowledgement (ACK). If it is tagged, the appliance 200 identifies orconfigures the port receiving the tagged SYN packet (SYN-ACK) as the“slow” side. In one embodiment, the appliance 200 optionally removes theACK tag from the packet before copying the packet to the other port. Ifthe LAN/WAN detector 238 determines that the packet is not tagged, theappliance 200 identifies or configure the port receiving the untaggedpacket as the “fast” side. The appliance 200 then tags the SYN packetwith an ACK and copies the packet to the other port.

In another embodiment, the LAN/WAN detector 238 detects fast and slowsides of a network using a SYN-ACK packet. The appliance 200 via theLAN/WAN detector 238 determines whether the SYN-ACK packet is taggedwith an acknowledgement (ACK). If it is tagged, the appliance 200identifies or configures the port receiving the tagged SYN packet(SYN-ACK) as the “slow” side. In one embodiment, the appliance 200optionally removes the ACK tag from the packet before copying the packetto the other port. If the LAN/WAN detector 238 determines that thepacket is not tagged, the appliance 200 identifies or configures theport receiving the untagged packet as the “fast” side. The LAN/WANdetector 238 determines whether the SYN packet was tagged. If the SYNpacket was not tagged, the appliance 200 copied the packet to the otherport. If the SYN packet was tagged, the appliance tags the SYN-ACKpacket before copying it to the other port.

The appliance 200, 200′ may add, insert, modify, attach or otherwiseprovide any information or data in the TCP option header to provide anyinformation, data or characteristics about the network connection,network traffic flow, or the configuration or operation of the appliance200. In this manner, not only does an appliance 200 announce itspresence to another appliance 200′ or tag a higher or lower speedconnection, the appliance 200 provides additional information and datavia the TCP option headers about the appliance or the connection. TheTCP option header information may be useful to or used by an appliancein controlling, managing, optimizing, acceleration or improving thenetwork traffic flow traversing the appliance 200, or to otherwiseconfigure itself or operation of a network port.

Although generally described in conjunction with detecting speeds ofnetwork connections or the presence of appliances, the LAN/WAN detector238 can be used for applying any type of function, logic or operation ofthe appliance 200 to a port, connection or flow of network traffic. Inparticular, automated assignment of ports can occur whenever a deviceperforms different functions on different ports, where the assignment ofa port to a task can be made during the unit's operation, and/or thenature of the network segment on each port is discoverable by theappliance 200.

Flow Control

The flow controller 220 includes any logic, business rules, function oroperations for optimizing, accelerating or otherwise improving theperformance, operation or quality of service of transport layercommunications of network packets or the delivery of packets at thetransport layer. A flow controller, also sometimes referred to as a flowcontrol module, regulates, manages and controls data transfer rates. Insome embodiments, the flow controller 220 is deployed at or connected ata bandwidth bottleneck in the network 104. In one embodiment, the flowcontroller 220 effectively regulates, manages and controls bandwidthusage or utilization. In other embodiments, the flow control modules mayalso be deployed at points on the network of latency transitions (lowlatency to high latency) and on links with media losses (such aswireless or satellite links).

In some embodiments, a flow controller 220 may include a receiver-sideflow control module for controlling the rate of receipt of networktransmissions and a sender-side flow control module for the controllingthe rate of transmissions of network packets. In other embodiments, afirst flow controller 220 includes a receiver-side flow control moduleand a second flow controller 220′ includes a sender-side flow controlmodule. In some embodiments, a first flow controller 220 is deployed ona first appliance 200 and a second flow controller 220′ is deployed on asecond appliance 200′. As such, in some embodiments, a first appliance200 controls the flow of data on the receiver side and a secondappliance 200′ controls the data flow from the sender side. In yetanother embodiment, a single appliance 200 includes flow control forboth the receiver-side and sender-side of network communicationstraversing the appliance 200.

In one embodiment, a flow control module 220 is configured to allowbandwidth at the bottleneck to be more fully utilized, and in someembodiments, not over-utilized. In some embodiments, the flow controlmodule 220 transparently buffers (or rebuffers data already buffered by,for example, the sender) network sessions that pass between nodes havingassociated flow control modules 220. When a session passes through twoor more flow control modules 220, one or more of the flow controlmodules controls a rate of the session(s).

In one embodiment, the flow control module 200 is configured withpredetermined data relating to bottleneck bandwidth. In anotherembodiment, the flow control module 220 may be configured to detect thebottleneck bandwidth or data associated therewith. Unlike conventionalnetwork protocols such as TCP, a receiver-side flow control module 220controls the data transmission rate. The receiver-side flow controlmodule controls 220 the sender-side flow control module, e.g., 220, datatransmission rate by forwarding transmission rate limits to thesender-side flow control module 220. In one embodiment, thereceiver-side flow control module 220 piggybacks these transmission ratelimits on acknowledgement (ACK) packets (or signals) sent to the sender,e.g., client 102, by the receiver, e.g., server 106. The receiver-sideflow control module 220 does this in response to rate control requeststhat are sent by the sender side flow control module 220′. The requestsfrom the sender-side flow control module 220′ may be “piggybacked” ondata packets sent by the sender 106.

In some embodiments, the flow controller 220 manipulates, adjusts,simulates, changes, improves or otherwise adapts the behavior of thetransport layer protocol to provide improved performance or operationsof delivery, data rates and/or bandwidth utilization of the transportlayer. The flow controller 220 may implement a plurality of data flowcontrol techniques at the transport layer, including but not limitedto 1) pre-acknowledgements, 2) window virtualization, 3) recongestiontechniques, 3) local retransmission techniques, 4) wavefront detectionand disambiguation, 5) transport control protocol selectiveacknowledgements, 6) transaction boundary detection techniques and 7)repacketization.

Although a sender may be generally described herein as a client 102 anda receiver as a server 106, a sender may be any end point such as aserver 106 or any computing device 100 on the network 104. Likewise, areceiver may be a client 102 or any other computing device on thenetwork 104.

Pre-Acknowledgements

In brief overview of a pre-acknowledgement flow control technique, theflow controller 220, in some embodiments, handles the acknowledgementsand retransmits for a sender, effectively terminating the sender'sconnection with the downstream portion of a network connection. Inreference to FIG. 1B, one possible deployment of an appliance 200 into anetwork architecture to implement this feature is depicted. In thisexample environment, a sending computer or client 102 transmits data onnetwork 104, for example, via a switch, which determines that the datais destined for VPN appliance 205. Because of the chosen networktopology, all data destined for VPN appliance 205 traverses appliance200, so the appliance 200 can apply any necessary algorithms to thisdata.

Continuing further with the example, the client 102 transmits a packet,which is received by the appliance 200. When the appliance 200 receivesthe packet, which is transmitted from the client 102 to a recipient viathe VPN appliance 205 the appliance 200 retains a copy of the packet andforwards the packet downstream to the VPN appliance 205. The appliance200 then generates an acknowledgement packet (ACK) and sends the ACKpacket back to the client 102 or sending endpoint. This ACK, apre-acknowledgment, causes the sender 102 to believe that the packet hasbeen delivered successfully, freeing the sender's resources forsubsequent processing. The appliance 200 retains the copy of the packetdata in the event that a retransmission of the packet is required, sothat the sender 102 does not have to handle retransmissions of the data.This early generation of acknowledgements may be called “preacking”.

If a retransmission of the packet is required, the appliance 200retransmits the packet to the sender. The appliance 200 may determinewhether retransmission is required as a sender would in a traditionalsystem, for example, determining that a packet is lost if anacknowledgement has not been received for the packet after apredetermined amount of time. To this end, the appliance 200 monitorsacknowledgements generated by the receiving endpoint, e.g., server 106(or any other downstream network entity) so that it can determinewhether the packet has been successfully delivered or needs to beretransmitted. If the appliance 200 determines that the packet has beensuccessfully delivered, the appliance 200 is free to discard the savedpacket data. The appliance 200 may also inhibit forwardingacknowledgements for packets that have already been received by thesending endpoint.

In the embodiment described above, the appliance 200 via the flowcontroller 220 controls the sender 102 through the delivery ofpre-acknowledgements, also referred to as “preacks”, as though theappliance 200 was a receiving endpoint itself. Since the appliance 200is not an endpoint and does not actually consume the data, the appliance200 includes a mechanism for providing overflow control to the sendingendpoint. Without overflow control, the appliance 200 could run out ofmemory because the appliance 200 stores packets that have been preackedto the sending endpoint but not yet acknowledged as received by thereceiving endpoint. Therefore, in a situation in which the sender 102transmits packets to the appliance 200 faster than the appliance 200 canforward the packets downstream, the memory available in the appliance200 to store unacknowledged packet data can quickly fill. A mechanismfor overflow control allows the appliance 200 to control transmission ofthe packets from the sender 102 to avoid this problem.

In one embodiment, the appliance 200 or flow controller 220 includes aninherent “self-clocking” overflow control mechanism. This self-clockingis due to the order in which the appliance 200 may be designed totransmit packets downstream and send ACKs to the sender 102 or 106. Insome embodiments, the appliance 200 does not preack the packet untilafter it transmits the packet downstream. In this way, the sender 102will receive the ACKs at the rate at which the appliance 200 is able totransmit packets rather than the rate at which the appliance 200receives packets from the sender 100. This helps to regulate thetransmission of packets from a sender 102.

Window Virtualization

Another overflow control mechanism that the appliance 200 may implementis to use the TCP window size parameter, which tells a sender how muchbuffer the receiver is permitting the sender to fill up. A nonzerowindow size (e.g., a size of at least one Maximum Segment Size (MSS)) ina preack permits the sending endpoint to continue to deliver data to theappliance, whereas a zero window size inhibits further datatransmission. Accordingly, the appliance 200 may regulate the flow ofpackets from the sender, for example when the appliance's 200 buffer isbecoming full, by appropriately setting the TCP window size in eachpreack.

Another technique to reduce this additional overhead is to applyhysteresis. When the appliance 200 delivers data to the slower side, theoverflow control mechanism in the appliance 200 can require that aminimum amount of space be available before sending a nonzero windowadvertisement to the sender. In one embodiment, the appliance 200 waitsuntil there is a minimum of a predetermined number of packets, such asfour packets, of space available before sending a nonzero window packet,such as a window size of four packet). This reduces the overhead byapproximately a factor four, since only two ACK packets are sent foreach group of four data packets, instead of eight ACK packets for fourdata packets.

Another technique the appliance 200 or flow controller 220 may use foroverflow control is the TCP delayed ACK mechanism, which skips ACKs toreduce network traffic. The TCP delayed

ACKs automatically delay the sending of an ACK, either until two packetsare received or until a fixed timeout has occurred. This mechanism alonecan result in cutting the overhead in half; moreover, by increasing thenumbers of packets above two, additional overhead reduction is realized.But merely delaying the ACK itself may be insufficient to controloverflow, and the appliance 200 may also use the advertised windowmechanism on the ACKs to control the sender. When doing this, theappliance 200 in one embodiment avoids triggering the timeout mechanismof the sender by delaying the ACK too long.

In one embodiment, the flow controller 220 does not preack the lastpacket of a group of packets. By not preacking the last packet, or atleast one of the packets in the group, the appliance avoids a falseacknowledgement for a group of packets. For example, if the appliancewere to send a preack for a last packet and the packet were subsequentlylost, the sender would have been tricked into thinking that the packetis delivered when it was not. Thinking that the packet had beendelivered, the sender could discard that data. If the appliance alsolost the packet, there would be no way to retransmit the packet to therecipient. By not preacking the last packet of a group of packets, thesender will not discard the packet until it has been delivered.

In another embodiment, the flow controller 220 may use a windowvirtualization technique to control the rate of flow or bandwidthutilization of a network connection. Though it may not immediately beapparent from examining conventional literature such as RFC 1323, thereis effectively a send window for transport layer protocols such as TCP.The send window is similar to the receive window, in that it consumesbuffer space (though on the sender). The sender's send window consistsof all data sent by the application that has not been acknowledged bythe receiver. This data must be retained in memory in caseretransmission is required. Since memory is a shared resource, some TCPstack implementations limit the size of this data. When the send windowis full, an attempt by an application program to send more data resultsin blocking the application program until space is available. Subsequentreception of acknowledgements will free send-window memory and unblockthe application program. In some embodiments, this window size is knownas the socket buffer size in some TCP implementations.

In one embodiment, the flow control module 220 is configured to provideaccess to increased window (or buffer) sizes. This configuration mayalso be referenced to as window virtualization. In the embodiment of TCPas the transport layer protocol, the TCP header includes a bit stringcorresponding to a window scale. In one embodiment, “window” may bereferenced in a context of send, receive, or both.

One embodiment of window virtualization is to insert a preackingappliance 200 into a TCP session. In reference to any of theenvironments of FIG. 1A or 1B, initiation of a data communicationsession between a source node, e.g., client 102 (for ease of discussion,now referenced as source node 102), and a destination node, e.g., server106 (for ease of discussion, now referenced as destination node 106) isestablished. For TCP communications, the source node 102 initiallytransmits a synchronization signal (“SYN”) through its local areanetwork 104 to first flow control module 220. The first flow controlmodule 220 inserts a configuration identifier into the TCP headeroptions area. The configuration identifier identifies this point in thedata path as a flow control module.

The appliances 200 via a flow control module 220 provide window (orbuffer) to allow increasing data buffering capabilities within a sessiondespite having end nodes with small buffer sizes, e.g., typically 16 kbytes. However, RFC 1323 requires window scaling for any buffer sizesgreater than 64 k bytes, which must be set at the time of sessioninitialization (SYN, SYN-ACK signals). Moreover, the window scalingcorresponds to the lowest common denominator in the data path, often anend node with small buffer size. This window scale often is a scale of 0or 1, which corresponds to a buffer size of up to 64 k or 128 k bytes.Note that because the window size is defined as the window field in eachpacket shifted over by the window scale, the window scale establishes anupper limit for the buffer, but does not guarantee the buffer isactually that large. Each packet indicates the current available bufferspace at the receiver in the window field.

In one embodiment of scaling using the window virtualization technique,during connection establishment (i.e., initialization of a session) whenthe first flow control module 220 receives from the source node 102 theSYN signal (or packet), the flow control module 220 stores the windowsscale of the source node 102 (which is the previous node) or stores a 0for window scale if the scale of the previous node is missing. The firstflow control module 220 also modifies the scale, e.g., increases thescale to 4 from 0 or 1, in the SYN-FCM signal. When the second flowcontrol module 220 receives the SYN signal, it stores the increasedscale from the first flow control signal and resets the scale in the SYNsignal back to the source node 103 scale value for transmission to thedestination node 106. When the second flow controller 220 receives theSYN-ACK signal from the destination node 106, it stores the scale fromthe destination node 106 scale, e.g., 0 or 1, and modifies it to anincreased scale that is sent with the SYN-ACK-FCM signal. The first flowcontrol node 220 receives and notes the received window scale andrevises the windows scale sent back to the source node 102 back down tothe original scale, e.g., 0 or 1. Based on the above window shiftconversation during connection establishment, the window field in everysubsequent packet, e.g., TCP packet, of the session must be shiftedaccording to the window shift conversion.

The window scale, as described above, expresses buffer sizes of over 64k and may not be required for window virtualization. Thus, shifts forwindow scale may be used to express increased buffer capacity in eachflow control module 220. This increase in buffer capacity in may bereferenced as window (or buffer) virtualization. The increase in buffersize allows greater packet through put from and to the respective endnodes 102 and 106. Note that buffer sizes in TCP are typically expressedin terms of bytes, but for ease of discussion “packets” may be used inthe description herein as it relates to virtualization.

By way of example, a window (or buffer) virtualization performed by theflow controller 220 is described. In this example, the source node 102and the destination node 106 are configured similar to conventional endnodes having a limited buffer capacity of 16 k bytes, which equalsapproximately 10 packets of data. Typically, an end node 102, 106 mustwait until the packet is transmitted and confirmation is received beforea next group of packets can be transmitted. In one embodiment, usingincreased buffer capacity in the flow control modules 220, when thesource node 103 transmits its data packets, the first flow controlmodule 220 receives the packets, stores it in its larger capacitybuffer, e.g., 512 packet capacity, and immediately sends back anacknowledgement signal indicating receipt of the packets (“REC-ACK”)back to the source node 102. The source node 102 can then “flush” itscurrent buffer, load it with 10 new data packets, and transmit thoseonto the first flow control module 220. Again, the first flow controlmodule 220 transmits a REC-ACK signal back to the source node 102 andthe source node 102 flushes its buffer and loads it with 10 more newpackets for transmission.

As the first flow control module 220 receives the data packets from thesource nodes, it loads up its buffer accordingly. When it is ready thefirst flow control module 220 can begin transmitting the data packets tothe second flow control module 230, which also has an increased buffersize, for example, to receive 512 packets. The second flow controlmodule 220′ receives the data packets and begins to transmit 10 packetsat a time to the destination node 106. Each REC-ACK received at thesecond flow control node 220 from the destination node 106 results in 10more packets being transmitted to the destination node 106 until all thedata packets are transferred. Hence, the present invention is able toincrease data transmission throughput between the source node (sender)102 and the destination node (receiver) 106 by taking advantage of thelarger buffer in the flow control modules 220, 220′ between the devices.

It is noted that by “preacking” the transmission of data as describedpreviously, a sender (or source node 102) is allowed to transmit moredata than is possible without the preacks, thus affecting a largerwindow size. For example, in one embodiment this technique is effectivewhen the flow control module 220, 220′ is located “near” a node (e.g.,source node 102 or destination node 106) that lacks large windows.

Recongestion

Another technique or algorithm of the flow controller 220 is referred toas recongestion. The standard TCP congestion avoidance algorithms areknown to perform poorly in the face of certain network conditions,including: large RTTs (round trip times), high packet loss rates, andothers. When the appliance 200 detects a congestion condition such aslong round trip times or high packet loss, the appliance 200 intervenes,substituting an alternate congestion avoidance algorithm that bettersuits the particular network condition. In one embodiment, therecongestion algorithm uses preacks to effectively terminate theconnection between the sender and the receiver. The appliance 200 thenresends the packets from itself to the receiver, using a differentcongestion avoidance algorithm. Recongestion algorithms may be dependenton the characteristics of the TCP connection. The appliance 200 monitorseach TCP connection, characterizing it with respect to the differentdimensions, selecting a recongestion algorithm that is appropriate forthe current characterization.

In one embodiment, upon detecting a TCP connection that is limited byround trip times (RTT), a recongestion algorithm is applied whichbehaves as multiple TCP connections. Each TCP connection operates withinits own performance limit but the aggregate bandwidth achieves a higherperformance level. One parameter in this mechanism is the number ofparallel connections that are applied (N). Too large a value of N andthe connection bundle achieves more than its fair share of bandwidth.Too small a value of N and the connection bundle achieves less than itsfair share of bandwidth. One method of establishing “N” relies on theappliance 200 monitoring the packet loss rate, RTT, and packet size ofthe actual connection. These numbers are plugged into a TCP responsecurve formula to provide an upper limit on the performance of a singleTCP connection in the present configuration. If each connection withinthe connection bundle is achieving substantially the same performance asthat computed to be the upper limit, then additional parallelconnections are applied. If the current bundle is achieving lessperformance than the upper limit, the number of parallel connections isreduced. In this manner, the overall fairness of the system ismaintained since individual connection bundles contain no moreparallelism than is required to eliminate the restrictions imposed bythe protocol itself. Furthermore, each individual connection retains TCPcompliance.

Another method of establishing “N” is to utilize a parallel flow controlalgorithm such as the TCP “Vegas” algorithm or its improved version“Stabilized Vegas.” In this method, the network information associatedwith the connections in the connection bundle (e.g., RTT, loss rate,average packet size, etc.) is aggregated and applied to the alternateflow control algorithm. The results of this algorithm are in turndistributed among the connections of the bundle controlling their number(i.e., N). Optionally, each connection within the bundle continues usingthe standard TCP congestion avoidance algorithm.

In another embodiment, the individual connections within a parallelbundle are virtualized, i.e., actual individual TCP connections are notestablished. Instead the congestion avoidance algorithm is modified tobehave as though there were N parallel connections. This method has theadvantage of appearing to transiting network nodes as a singleconnection. Thus the QOS, security and other monitoring methods of thesenodes are unaffected by the recongestion algorithm. In yet anotherembodiment, the individual connections within a parallel bundle arereal, i.e., a separate. TCP connection is established for each of theparallel connections within a bundle. The congestion avoidance algorithmfor each TCP connection need not be modified.

Retransmission

In some embodiments, the flow controller 220 may apply a localretransmission technique. One reason for implementing preacks is toprepare to transit a high-loss link (e.g., wireless). In theseembodiments, the preacking appliance 200 or flow control module 220 islocated most beneficially “before” the wireless link. This allowsretransmissions to be performed closer to the high loss link, removingthe retransmission burden from the remainder of the network. Theappliance 200 may provide local retransmission, in which case, packetsdropped due to failures of the link are retransmitted directly by theappliance 200. This is advantageous because it eliminates theretransmission burden upon an end node, such as server 106, andinfrastructure of any of the networks 104. With appliance 200 providinglocal retransmissions, the dropped packet can be retransmitted acrossthe high loss link without necessitating a retransmit by an end node anda corresponding decrease in the rate of data transmission from the endnode.

Another reason for implementing preacks is to avoid a receive time out(RTO) penalty. In standard TCP there are many situations that result inan RTO, even though a large percentage of the packets in flight weresuccessfully received. With standard TCP algorithms, dropping more thanone packet within an RTT window would likely result in a timeout.Additionally, most TCP connections experience a timeout if aretransmitted packet is dropped. In a network with a high bandwidthdelay product, even a relatively small packet loss rate will causefrequent Retransmission timeouts (RTOs). In one embodiment, theappliance 200 uses a retransmit and timeout algorithm is avoid prematureRTOs. The appliance 200 or flow controller 220 maintains a count ofretransmissions is maintained on a per-packet basis. Each time that apacket is retransmitted, the count is incremented by one and theappliance 200 continues to transmit packets. In some embodiments, onlyif a packet has been retransmitted a predetermined number of times is anRTO declared.

Wavefront Detection and Disambiguation

In some embodiments, the appliance 200 or flow controller 220 useswavefront detection and disambiguation techniques in managing andcontrolling flow of network traffic. In this technique, the flowcontroller 220 uses transmit identifiers or numbers to determine whetherparticular data packets need to be retransmitted. By way of example, asender transmits data packets over a network, where each instance of atransmitted data packet is associated with a transmit number. It can beappreciated that the transmit number for a packet is not the same as thepacket's sequence number, since a sequence number references the data inthe packet while the transmit number references an instance of atransmission of that data. The transmit number can be any informationusable for this purpose, including a timestamp associated with a packetor simply an increasing number (similar to a sequence number or a packetnumber). Because a data segment may be retransmitted, different transmitnumbers may be associated with a particular sequence number.

As the sender transmits data packets, the sender maintains a datastructure of acknowledged instances of data packet transmissions. Eachinstance of a data packet transmission is referenced by its sequencenumber and transmit number. By maintaining a transmit number for eachpacket, the sender retains the ordering of the transmission of datapackets. When the sender receives an ACK or a SACK, the senderdetermines the highest transmit number associated with packets that thereceiver indicated has arrived (in the received acknowledgement). Anyoutstanding unacknowledged packets with lower transmit numbers arepresumed lost.

In some embodiments, the sender is presented with an ambiguous situationwhen the arriving packet has been retransmitted: a standard ACK/SACKdoes not contain enough information to allow the sender to determinewhich transmission of the arriving packet has triggered theacknowledgement. After receiving an ambiguous acknowledgement,therefore, the sender disambiguates the acknowledgement to associate itwith a transmit number. In various embodiments, one or a combination ofseveral techniques may be used to resolve this ambiguity.

In one embodiment, the sender includes an identifier with a transmitteddata packet, and the receiver returns that identifier or a functionthereof with the acknowledgement. The identifier may be a timestamp(e.g., a TCP timestamp as described in RFC 1323), a sequential number,or any other information that can be used to resolve between two or moreinstances of a packet's transmission. In an embodiment in which the TCPtimestamp option is used to disambiguate the acknowledgement, eachpacket is tagged with up to 32-bits of unique information. Upon receiptof the data packet, the receiver echoes this unique information back tothe sender with the acknowledgement. The sender ensures that theoriginally sent packet and its retransmitted version or versions containdifferent values for the timestamp option, allowing it to unambiguouslyeliminate the ACK ambiguity. The sender may maintain this uniqueinformation, for example, in the data structure in which it stores thestatus of sent data packets. This technique is advantageous because itcomplies with industry standards and is thus likely to encounter littleor no interoperability issues. However, this technique may require tenbytes of TCP header space in some implementations, reducing theeffective throughput rate on the network and reducing space availablefor other TCP options.

In another embodiment, another field in the packet, such as the IP IDfield, is used to disambiguate in a way similar to the TCP timestampoption described above. The sender arranges for the ID field values ofthe original and the retransmitted version or versions of the packet tohave different ID fields in the IP header. Upon reception of the datapacket at the receiver, or a proxy device thereof, the receiver sets theID field of the ACK packet to a function of the ID field of the packetthat triggers the ACK. This method is advantageous, as it requires noadditional data to be sent, preserving the efficiency of the network andTCP header space. The function chosen should provide a high degree oflikelihood of providing disambiguation. In a preferred embodiment, thesender selects IP ID values with the most significant bit set to 0. Whenthe receiver responds, the IP ID value is set to the same IP ID valuewith the most significant bit set to a one.

In another embodiment, the transmit numbers associated withnon-ambiguous acknowledgements are used to disambiguate an ambiguousacknowledgement. This technique is based on the principle thatacknowledgements for two packets will tend to be received closer in timeas the packets are transmitted closer in time. Packets that are notretransmitted will not result in ambiguity, as the acknowledgementsreceived for such packets can be readily associated with a transmitnumber. Therefore, these known transmit numbers are compared to thepossible transmit numbers for an ambiguous acknowledgement received nearin time to the known acknowledgement. The sender compares the transmitnumbers of the ambiguous acknowledgement against the last known receivedtransmit number, selecting the one closest to the known receivedtransmit number. For example, if an acknowledgement for data packet 1 isreceived and the last received acknowledgement was for data packet 5,the sender resolves the ambiguity by assuming that the third instance ofdata packet 1 caused the acknowledgement.

Selective Acknowledgements

Another technique of the appliance 200 or flow controller 220 is toimplement an embodiment of transport control protocol selectiveacknowledgements, or TCP SACK, to determine what packets have or havenot been received. This technique allows the sender to determineunambiguously a list of packets that have been received by the receiveras well as an accurate list of packets not received. This functionalitymay be implemented by modifying the sender and/or receiver, or byinserting sender- and receiver-side flow control modules 220 in thenetwork path between the sender and receiver. In reference to FIG. 1A orFIG. 1B, a sender, e.g., client 102, is configured to transmit datapackets to the receiver, e.g., server 106, over the network 104. Inresponse, the receiver returns a TCP Selective Acknowledgment option,referred to as SACK packet to the sender. In one embodiment, thecommunication is bi-directional, although only one direction ofcommunication is discussed here for simplicity. The receiver maintains alist, or other suitable data structure, that contains a group of rangesof sequence numbers for data packets that the receiver has actuallyreceived. In some embodiments, the list is sorted by sequence number inan ascending or descending order. The receiver also maintains a left-offpointer, which comprises a reference into the list and indicates theleft-off point from the previously generated SACK packet.

Upon reception of a data packet, the receiver generates and transmits aSACK packet back to the sender. In some embodiments, the SACK packetincludes a number of fields, each of which can hold a range of sequencenumbers to indicate a set of received data packets. The receiver fillsthis first field of the SACK packet with a range of sequence numbersthat includes the landing packet that triggered the SACK packet. Theremaining available SACK fields are filled with ranges of sequencenumbers from the list of received packets. As there are more ranges inthe list than can be loaded into the SACK packet, the receiver uses theleft-off pointer to determine which ranges are loaded into the SACKpacket. The receiver inserts the SACK ranges consecutively from thesorted list, starting from the range referenced by the pointer andcontinuing down the list until the available SACK range space in the TCPheader of the SACK packet is consumed. The receiver wraps around to thestart of the list if it reaches the end. In some embodiments, two orthree additional SACK ranges can be added to the SACK range information.

Once the receiver generates the SACK packet, the receiver sends theacknowledgement back to the sender. The receiver then advances theleft-off pointer by one or more SACK range entries in the list. If thereceiver inserts four SACK ranges, for example, the left-off pointer maybe advanced two SACK ranges in the list. When the advanced left-offpointer reaches at the end of the list, the pointer is reset to thestart of the list, effectively wrapping around the list of knownreceived ranges. Wrapping around the list enables the system to performwell, even in the presence of large losses of SACK packets, since theSACK information that is not communicated due to a lost SACK packet willeventually be communicated once the list is wrapped around.

It can be appreciated, therefore, that a SACK packet may communicateseveral details about the condition of the receiver. First, the SACKpacket indicates that, upon generation of the SACK packet, the receiverhad just received a data packet that is within the first field of theSACK information. Secondly, the second and subsequent fields of the SACKinformation indicate that the receiver has received the data packetswithin those ranges. The SACK information also implies that the receiverhad not, at the time of the SACK packet's generation, received any ofthe data packets that fall between the second and subsequent fields ofthe SACK information. In essence, the ranges between the second andsubsequent ranges in the SACK information are “holes” in the receiveddata, the data therein known not to have been delivered. Using thismethod, therefore, when a SACK packet has sufficient space to includemore than two SACK ranges, the receiver may indicate to the sender arange of data packets that have not yet been received by the receiver.

In another embodiment, the sender uses the SACK packet described abovein combination with the retransmit technique described above to makeassumptions about which data packets have been delivered to thereceiver. For example, when the retransmit algorithm (using the transmitnumbers) declares a packet lost, the sender considers the packet to beonly conditionally lost, as it is possible that the SACK packetidentifying the reception of this packet was lost rather than the datapacket itself. The sender thus adds this packet to a list of potentiallylost packets, called the presumed lost list. Each time a SACK packetarrives, the known missing ranges of data from the SACK packet arecompared to the packets in the presumed lost list. Packets that containdata known to be missing are declared actually lost and are subsequentlyretransmitted. In this way, the two schemes are combined to give thesender better information about which packets have been lost and need tobe retransmitted.

Transaction Boundary Detection

In some embodiments, the appliance 200 or flow controller 220 applies atechnique referred to as transaction boundary detection. In oneembodiment, the technique pertains to ping-pong behaved connections. Atthe TCP layer, ping-pong behavior is when one communicant—a sender-sendsdata and then waits for a response from the other communicant—thereceiver. Examples of ping-pong behavior include remote procedure call,HTTP and others. The algorithms described above use retransmissiontimeout (RTO) to recover from the dropping of the last packet or packetsassociated with the transaction. Since the TCP RTO mechanism isextremely coarse in some embodiments, for example requiring a minimumone second value in all cases), poor application behavior may be seen inthese situations.

In one embodiment, the sender of data or a flow control module 220coupled to the sender detects a transaction boundary in the data beingsent. Upon detecting a transaction boundary, the sender or a flowcontrol module 220 sends additional packets, whose reception generatesadditional ACK or SACK responses from the receiver. Insertion of theadditional packets is preferably limited to balance between improvedapplication response time and network capacity utilization. The numberof additional packets that is inserted may be selected according to thecurrent loss rate associated with that connection, with more packetsselected for connections having a higher loss rate.

One method of detecting a transaction boundary is time based. If thesender has been sending data and ceases, then after a period of time thesender or flow control module 200 declares a transaction boundary. Thismay be combined with other techniques. For example, the setting of thePSH (TCP Push) bit by the sender in the TCP header may indicate atransaction boundary. Accordingly, combining the time-based approachwith these additional heuristics can provide for more accurate detectionof a transaction boundary. In another technique, if the sender or flowcontrol module 220 understands the application protocol, it can parsethe protocol data stream and directly determine transaction boundaries.In some embodiment, this last behavior can be used independent of anytime-based mechanism.

Responsive to detecting a transaction boundary, the sender or flowcontrol module 220 transmits additional data packets to the receiver tocause acknowledgements therefrom. The additional data packets shouldtherefore be such that the receiver will at least generate an ACK orSACK in response to receiving the data packet. In one embodiment, thelast packet or packets of the transaction are simply retransmitted. Thishas the added benefit of retransmitting needed data if the last packetor packets had been dropped, as compared to merely sending dummy datapackets. In another embodiment, fractions of the last packet or packetsare sent, allowing the sender to disambiguate the arrival of thesepackets from their original packets. This allows the receiver to avoidfalsely confusing any reordering adaptation algorithms. In anotherembodiment, any of a number of well-known forward error correctiontechniques can be used to generate additional data for the insertedpackets, allowing for the reconstruction of dropped or otherwise missingdata at the receiver.

In some embodiments, the boundary detection technique described hereinhelps to avoid a timeout when the acknowledgements for the last datapackets in a transaction are dropped. When the sender or flow controlmodule 220 receives the acknowledgements for these additional datapackets, the sender can determine from these additional acknowledgementswhether the last data packets have been received or need to beretransmitted, thus avoiding a timeout. In one embodiment, if the lastpackets have been received but their acknowledgements were dropped, aflow control module 220 generates an acknowledgement for the datapackets and sends the acknowledgement to the sender, thus communicatingto the sender that the data packets have been delivered. In anotherembodiment, if the last packets have not been received, a flow controlmodule 200 sends a packet to the sender to cause the sender toretransmit the dropped data packets.

Repacketization

In yet another embodiment, the appliance 200 or flow controller 220applies a repacketization technique for improving the flow of transportlayer network traffic. In some embodiments, performance of TCP isproportional to packet size. Thus increasing packet sizes improvesperformance unless it causes substantially increased packet loss ratesor other nonlinear effects, like IP fragmentation. In general, wiredmedia (such as copper or fibre optics) have extremely low bit-errorrates, low enough that these can be ignored. For these media, it isadvantageous for the packet size to be the maximum possible beforefragmentation occurs (the maximum packet size is limited by theprotocols of the underlying transmission media). Whereas fortransmission media with higher loss rates (e.g., wireless technologiessuch as WiFi, etc., or high-loss environments such as power-linenetworking, etc.), increasing the packet size may lead to lowertransmission rates, as media-induced errors cause an entire packet to bedropped (i.e., media-induced errors beyond the capability of thestandard error correcting code for that media), increasing the packetloss rate. A sufficiently large increase in the packet loss rate willactually negate any performance benefit of increasing packet size. Insome cases, it may be difficult for a TCP endpoint to choose an optimalpacket size. For example, the optimal packet size may vary across thetransmission path, depending on the nature of each link.

By inserting an appliance 200 or flow control module 220 into thetransmission path, the flow controller 220 monitors characteristics ofthe link and repacketizes according to determined link characteristics.In one embodiment, an appliance 200 or flow controller 220 repacketizespackets with sequential data into a smaller number of larger packets. Inanother embodiment, an appliance 200 or flow controller 220 repacketizespackets by breaking part a sequence of large packets into a largernumber of smaller packets. In other embodiments, an appliance 200 orflow controller 220 monitors the link characteristics and adjusts thepacket sizes through recombination to improve throughput.

QoS

Still referring to FIG. 2A, the flow controller 220, in someembodiments, may include a QoS Engine 236, also referred to as a QoScontroller. In another embodiment, the appliance 200 and/or networkoptimization engine 250 includes the QoS engine 236, for example,separately but in communication with the flow controller 220. The QoSEngine 236 includes any logic, business rules, function or operationsfor performing one or more Quality of Service (QoS) techniques improvingthe performance, operation or quality of service of any of the networkconnections. In some embodiments, the QoS engine 236 includes networktraffic control and management mechanisms that provide differentpriorities to different users, applications, data flows or connections.In other embodiments, the QoS engine 236 controls, maintains, or assuresa certain level of performance to a user, application, data flow orconnection. In one embodiment, the QoS engine 236 controls, maintains orassures a certain portion of bandwidth or network capacity for a user,application, data flow or connection. In some embodiments, the QoSengine 236 monitors the achieved level of performance or the quality ofservice corresponding to a user, application, data flow or connection,for example, the data rate and delay. In response to monitoring, the QoSengine 236 dynamically controls or adjusts scheduling priorities ofnetwork packets to achieve the desired level of performance or qualityof service.

In some embodiments, the QoS engine 236 prioritizes, schedules andtransmits network packets according to one or more classes or levels ofservices. In some embodiments, the class or level service mayinclude: 1) best efforts, 2) controlled load, 3) guaranteed or 4)qualitative. For a best efforts class of service, the appliance 200makes reasonable effort to deliver packets (a standard service level).For a controlled load class of service, the appliance 200 or QoS engine236 approximates the standard packet error loss of the transmissionmedium or approximates the behavior of best-effort service in lightlyloaded network conditions. For a guaranteed class of service, theappliance 200 or QoS engine 236 guarantees the ability to transmit dataat a determined rate for the duration of the connection. For aqualitative class of service, the appliance 200 or QoS engine 236 thequalitative service class is used for applications, users, data flows orconnection that require or desire prioritized traffic but cannotquantify resource needs or level of service. In these cases, theappliance 200 or QoS engine 236 determines the class of service orprioritization based on any logic or configuration of the QoS engine 236or based on business rules or policies. For example, in one embodiment,the QoS engine 236 prioritizes, schedules and transmits network packetsaccording to one or more policies as specified by the policy engine 295,295′.

Protocol Acceleration

The protocol accelerator 234 includes any logic, business rules,function or operations for optimizing, accelerating, or otherwiseimproving the performance, operation or quality of service of one ormore protocols. In one embodiment, the protocol accelerator 234accelerates any application layer protocol or protocols at layers 5-7 ofthe network stack. In other embodiments, the protocol accelerator 234accelerates a transport layer or a layer 4 protocol. In one embodiment,the protocol accelerator 234 accelerates layer 2 or layer 3 protocols.In some embodiments, the protocol accelerator 234 is configured,constructed or designed to optimize or accelerate each of one or moreprotocols according to the type of data, characteristics and/or behaviorof the protocol. In another embodiment, the protocol accelerator 234 isconfigured, constructed or designed to improve a user experience,response times, network or computer load, and/or network or bandwidthutilization with respect to a protocol.

In one embodiment, the protocol accelerator 234 is configured,constructed or designed to minimize the effect of WAN latency on filesystem access. In some embodiments, the protocol accelerator 234optimizes or accelerates the use of the CIFS (Common Internet FileSystem) protocol to improve file system access times or access times todata and files. In some embodiments, the protocol accelerator 234optimizes or accelerates the use of the NFS (Network File System)protocol. In another embodiment, the protocol accelerator 234 optimizesor accelerates the use of the File Transfer protocol (FTP).

In one embodiment, the protocol accelerator 234 is configured,constructed or designed to optimize or accelerate a protocol carrying asa payload or using any type and form of markup language. In otherembodiments, the protocol accelerator 234 is configured, constructed ordesigned to optimize or accelerate a HyperText Transfer Protocol (HTTP).In another embodiment, the protocol accelerator 234 is configured,constructed or designed to optimize or accelerate a protocol carrying asa payload or otherwise using XML (eXtensible Markup Language).

Transparency and Multiple Deployment Configuration

In some embodiments, the appliance 200 and/or network optimizationengine 250 is transparent to any data flowing across a networkconnection or link, such as a WAN link. In one embodiment, the appliance200 and/or network optimization engine 250 operates in such a mannerthat the data flow across the WAN is recognizable by any networkmonitoring, QOS management or network analysis tools. In someembodiments, the appliance 200 and/or network optimization engine 250does not create any tunnels or streams for transmitting data that mayhide, obscure or otherwise make the network traffic not transparent. Inother embodiments, the appliance 200 operates transparently in that theappliance does not change any of the source and/or destination addressinformation or port information of a network packet, such as internetprotocol addresses or port numbers. In other embodiments, the appliance200 and/or network optimization engine 250 is considered to operate orbehave transparently to the network, an application, client, server orother appliances or computing device in the network infrastructure. Thatis, in some embodiments, the appliance is transparent in that networkrelated configuration of any device or appliance on the network does notneed to be modified to support the appliance 200.

The appliance 200 may be deployed in any of the following deploymentconfigurations: 1) in-line of traffic, 2) in proxy mode, or 3) in avirtual in-line mode. In some embodiments, the appliance 200 may bedeployed inline to one or more of the following: a router, a client, aserver or another network device or appliance. In other embodiments, theappliance 200 may be deployed in parallel to one or more of thefollowing: a router, a client, a server or another network device orappliance. In parallel deployments, a client, server, router or othernetwork appliance may be configured to forward, transfer or transitnetworks to or via the appliance 200.

In the embodiment of in-line, the appliance 200 is deployed inline witha WAN link of a router. In this way, all traffic from the WAN passesthrough the appliance before arriving at a destination of a LAN.

In the embodiment of a proxy mode, the appliance 200 is deployed as aproxy device between a client and a server. In some embodiments, theappliance 200 allows clients to make indirect connections to a resourceon a network. For example, a client connects to a resource via theappliance 200, and the appliance provides the resource either byconnecting to the resource, a different resource, or by serving theresource from a cache. In some cases, the appliance may alter theclient's request or the server's response for various purposes, such asfor any of the optimization techniques discussed herein. In otherembodiments, the appliance 200 behaves as a transparent proxy, byintercepting and forwarding requests and responses transparently to aclient and/or server. Without client-side configuration, the appliance200 may redirect client requests to different servers or networks. Insome embodiments, the appliance 200 may perform any type and form ofnetwork address translation, referred to as NAT, on any network traffictraversing the appliance.

In some embodiments, the appliance 200 is deployed in a virtual in-linemode configuration. In this embodiment, a router or a network devicewith routing or switching functionality is configured to forward,reroute or otherwise provide network packets destined to a network tothe appliance 200. The appliance 200 then performs any desiredprocessing on the network packets, such as any of the WAN optimizationtechniques discussed herein. Upon completion of processing, theappliance 200 forwards the processed network packet to the router totransmit to the destination on the network. In this way, the appliance200 can be coupled to the router in parallel but still operate as it ifthe appliance 200 were inline. This deployment mode also providestransparency in that the source and destination addresses and portinformation are preserved as the packet is processed and transmitted viathe appliance through the network.

End Node Deployment

Although the network optimization engine 250 is generally describedabove in conjunction with an appliance 200, the network optimizationengine 250, or any portion thereof, may be deployed, distributed orotherwise operated on any end node, such as a client 102 and/or server106. As such, a client or server may provide any of the systems andmethods of the network optimization engine 250 described herein inconjunction with one or more appliances 200 or without an appliance 200.

Referring now to FIG. 2B, an example embodiment of the networkoptimization engine 250 deployed on one or more end nodes is depicted.In brief overview, the client 102 may include a first networkoptimization engine 250′ and the server 106 may include a second networkoptimization engine 250″. The client 102 and server 106 may establish atransport layer connection and exchange communications with or withouttraversing an appliance 200.

In one embodiment, the network optimization engine 250′ of the client102 performs the techniques described herein to optimize, accelerate orotherwise improve the performance, operation or quality of service ofnetwork traffic communicated with the server 106. In another embodiment,the network optimization engine 250″ of the server 106 performs thetechniques described herein to optimize, accelerate or otherwise improvethe performance, operation or quality of service of network trafficcommunicated with the client 102. In some embodiments, the networkoptimization engine 250′ of the client 102 and the network optimizationengine 250″ of the server 106 perform the techniques described herein tooptimize, accelerate or otherwise improve the performance, operation orquality of service of network traffic communicated between the client102 and the server 106. In yet another embodiment, the networkoptimization engine 250′ of the client 102 performs the techniquesdescribed herein in conjunction with an appliance 200 to optimize,accelerate or otherwise improve the performance, operation or quality ofservice of network traffic communicated with the client 102. In stillanother embodiment, the network optimization engine 250″ of the server106 performs the techniques described herein in conjunction with anappliance 200 to optimize, accelerate or otherwise improve theperformance, operation or quality of service of network trafficcommunicated with the server 106.

C. Client Agent

Referring now to FIG. 3, an embodiment of a client agent 120 isdepicted. The client 102 has a client agent 120 for establishing,exchanging, managing or controlling communications with the appliance200, appliance 205 and/or server 106 via a network 104. In someembodiments, the client agent 120, which may also be referred to as aWAN client, accelerates WAN network communications and/or is used tocommunicate via appliance 200 on a network. In brief overview, theclient 102 operates on computing device 100 having an operating systemwith a kernel mode 302 and a user mode 303, and a network stack 267 withone or more layers 310 a-310 b. The client 102 may have installed and/orexecute one or more applications. In some embodiments, one or moreapplications may communicate via the network stack 267 to a network 104.One of the applications, such as a web browser, may also include a firstprogram 322. For example, the first program 322 may be used in someembodiments to install and/or execute the client agent 120, or anyportion thereof. The client agent 120 includes an interceptionmechanism, or interceptor 350, for intercepting network communicationsfrom the network stack 267 from the one or more applications.

As with the appliance 200, the client has a network stack 267 includingany type and form of software, hardware, or any combinations thereof,for providing connectivity to and communications with a network 104. Thenetwork stack 267 of the client 102 includes any of the network stackembodiments described above in conjunction with the appliance 200. Insome embodiments, the client agent 120, or any portion thereof, isdesigned and constructed to operate with or work in conjunction with thenetwork stack 267 installed or otherwise provided by the operatingsystem of the client 102.

In further details, the network stack 267 of the client 102 or appliance200 (or 205) may include any type and form of interfaces for receiving,obtaining, providing or otherwise accessing any information and datarelated to network communications of the client 102. In one embodiment,an interface to the network stack 267 includes an applicationprogramming interface (API). The interface may also have any functioncall, hooking or filtering mechanism, event or call back mechanism, orany type of interfacing technique. The network stack 267 via theinterface may receive or provide any type and form of data structure,such as an object, related to functionality or operation of the networkstack 267. For example, the data structure may include information anddata related to a network packet or one or more network packets. In someembodiments, the data structure includes, references or identifies aportion of the network packet processed at a protocol layer of thenetwork stack 267, such as a network packet of the transport layer. Insome embodiments, the data structure 325 is a kernel-level datastructure, while in other embodiments, the data structure 325 is auser-mode data structure. A kernel-level data structure may have a datastructure obtained or related to a portion of the network stack 267operating in kernel-mode 302, or a network driver or other softwarerunning in kernel-mode 302, or any data structure obtained or receivedby a service, process, task, thread or other executable instructionsrunning or operating in kernel-mode of the operating system.

Additionally, some portions of the network stack 267 may execute oroperate in kernel-mode 302, for example, the data link or network layer,while other portions execute or operate in user-mode 303, such as anapplication layer of the network stack 267. For example, a first portion310 a of the network stack may provide user-mode access to the networkstack 267 to an application while a second portion 310 a of the networkstack 267 provides access to a network. In some embodiments, a firstportion 310 a of the network stack has one or more upper layers of thenetwork stack 267, such as any of layers 5-7. In other embodiments, asecond portion 310 b of the network stack 267 includes one or more lowerlayers, such as any of layers 1-4. Each of the first portion 310 a andsecond portion 310 b of the network stack 267 may include any portion ofthe network stack 267, at any one or more network layers, in user-mode303, kernel-mode, 302, or combinations thereof, or at any portion of anetwork layer or interface point to a network layer or any portion of orinterface point to the user-mode 302 and kernel-mode 203.

The interceptor 350 may include software, hardware, or any combinationof software and hardware. In one embodiment, the interceptor 350intercepts or otherwise receives a network communication at any point inthe network stack 267, and redirects or transmits the networkcommunication to a destination desired, managed or controlled by theinterceptor 350 or client agent 120. For example, the interceptor 350may intercept a network communication of a network stack 267 of a firstnetwork and transmit the network communication to the appliance 200 fortransmission on a second network 104. In some embodiments, theinterceptor 350 includes or is a driver, such as a network driverconstructed and designed to interface and work with the network stack267. In some embodiments, the client agent 120 and/or interceptor 350operates at one or more layers of the network stack 267, such as at thetransport layer. In one embodiment, the interceptor 350 includes afilter driver, hooking mechanism, or any form and type of suitablenetwork driver interface that interfaces to the transport layer of thenetwork stack, such as via the transport driver interface (TDI). In someembodiments, the interceptor 350 interfaces to a first protocol layer,such as the transport layer and another protocol layer, such as anylayer above the transport protocol layer, for example, an applicationprotocol layer. In one embodiment, the interceptor 350 includes a drivercomplying with the Network Driver Interface Specification (NDIS), or aNDIS driver. In another embodiment, the interceptor 350 may be amin-filter or a mini-port driver. In one embodiment, the interceptor350, or portion thereof, operates in kernel-mode 202. In anotherembodiment, the interceptor 350, or portion thereof, operates inuser-mode 203. In some embodiments, a portion of the interceptor 350operates in kernel-mode 202 while another portion of the interceptor 350operates in user-mode 203. In other embodiments, the client agent 120operates in user-mode 203 but interfaces via the interceptor 350 to akernel-mode driver, process, service, task or portion of the operatingsystem, such as to obtain a kernel-level data structure 225. In furtherembodiments, the interceptor 350 is a user-mode application or program,such as application.

In one embodiment, the interceptor 350 intercepts or receives anytransport layer connection requests. In these embodiments, theinterceptor 350 executes transport layer application programminginterface (API) calls to set the destination information, such asdestination IP address and/or port to a desired location for thelocation. In this manner, the interceptor 350 intercepts and redirectsthe transport layer connection to an IP address and port controlled ormanaged by the interceptor 350 or client agent 120. In one embodiment,the interceptor 350 sets the destination information for the connectionto a local IP address and port of the client 102 on which the clientagent 120 is listening. For example, the client agent 120 may comprise aproxy service listening on a local IP address and port for redirectedtransport layer communications. In some embodiments, the client agent120 then communicates the redirected transport layer communication tothe appliance 200.

In some embodiments, the interceptor 350 intercepts a Domain NameService (DNS) request. In one embodiment, the client agent 120 and/orinterceptor 350 resolves the DNS request. In another embodiment, theinterceptor transmits the intercepted DNS request to the appliance 200for DNS resolution. In one embodiment, the appliance 200 resolves theDNS request and communicates the DNS response to the client agent 120.In some embodiments, the appliance 200 resolves the DNS request viaanother appliance 200′ or a DNS server 106.

In yet another embodiment, the client agent 120 may include two agents120 and 120′. In one embodiment, a first agent 120 may include aninterceptor 350 operating at the network layer of the network stack 267.In some embodiments, the first agent 120 intercepts network layerrequests such as Internet Control Message Protocol (ICMP) requests(e.g., ping and traceroute). In other embodiments, the second agent 120′may operate at the transport layer and intercept transport layercommunications. In some embodiments, the first agent 120 interceptscommunications at one layer of the network stack 210 and interfaces withor communicates the intercepted communication to the second agent 120′.

The client agent 120 and/or interceptor 350 may operate at or interfacewith a protocol layer in a manner transparent to any other protocollayer of the network stack 267. For example, in one embodiment, theinterceptor 350 operates or interfaces with the transport layer of thenetwork stack 267 transparently to any protocol layer below thetransport layer, such as the network layer, and any protocol layer abovethe transport layer, such as the session, presentation or applicationlayer protocols. This allows the other protocol layers of the networkstack 267 to operate as desired and without modification for using theinterceptor 350. As such, the client agent 120 and/or interceptor 350can interface with the transport layer to secure, optimize, accelerate,route or load-balance any communications provided via any protocolcarried by the transport layer, such as any application layer protocolover TCP/IP.

Furthermore, the client agent 120 and/or interceptor 350 may operate ator interface with the network stack 267 in a manner transparent to anyapplication, a user of the client 102, the client 102 and/or any othercomputing device 100, such as a server or appliance 200, 206, incommunications with the client 102. The client agent 120, or any portionthereof, may be installed and/or executed on the client 102 in a mannerwithout modification of an application. In one embodiment, the clientagent 120, or any portion thereof, is installed and/or executed in amanner transparent to any network configuration of the client 102,appliance 200, 205 or server 106. In some embodiments, the client agent120, or any portion thereof, is installed and/or executed withmodification to any network configuration of the client 102, appliance200, 205 or server 106. In one embodiment, the user of the client 102 ora computing device in communications with the client 102 are not awareof the existence, execution or operation of the client agent 12, or anyportion thereof. As such, in some embodiments, the client agent 120and/or interceptor 350 is installed, executed, and/or operatedtransparently to an application, user of the client 102, the client 102,another computing device, such as a server or appliance 200, 2005, orany of the protocol layers above and/or below the protocol layerinterfaced to by the interceptor 350.

The client agent 120 includes a streaming client 306, a collection agent304, SSL VPN agent 308, a network optimization engine 250, and/oracceleration program 302. In one embodiment, the client agent 120 is anIndependent Computing Architecture (ICA) client, or any portion thereof,developed by Citrix Systems, Inc. of Fort Lauderdale, Fla., and is alsoreferred to as an ICA client. In some embodiments, the client agent 120has an application streaming client 306 for streaming an applicationfrom a server 106 to a client 102. In another embodiment, the clientagent 120 includes a collection agent 304 for performing end-pointdetection/scanning and collecting end-point information for theappliance 200 and/or server 106. In some embodiments, the client agent120 has one or more network accelerating or optimizing programs oragents, such as an network optimization engine 250 and an accelerationprogram 302. In one embodiment, the acceleration program 302 acceleratescommunications between client 102 and server 106 via appliance 205′. Insome embodiments, the network optimization engine 250 provides WANoptimization techniques as discussed herein.

The streaming client 306 is an application, program, process, service,task or set of executable instructions for receiving and executing astreamed application from a server 106. A server 106 may stream one ormore application data files to the streaming client 306 for playing,executing or otherwise causing to be executed the application on theclient 102. In some embodiments, the server 106 transmits a set ofcompressed or packaged application data files to the streaming client306. In some embodiments, the plurality of application files arecompressed and stored on a file server within an archive file such as aCAB, ZIP, SIT, TAR, JAR or other archive. In one embodiment, the server106 decompresses, unpackages or unarchives the application files andtransmits the files to the client 102. In another embodiment, the client102 decompresses, unpackages or unarchives the application files. Thestreaming client 306 dynamically installs the application, or portionthereof, and executes the application. In one embodiment, the streamingclient 306 may be an executable program. In some embodiments, thestreaming client 306 may be able to launch another executable program.

The collection agent 304 is an application, program, process, service,task or set of executable instructions for identifying, obtaining and/orcollecting information about the client 102. In some embodiments, theappliance 200 transmits the collection agent 304 to the client 102 orclient agent 120. The collection agent 304 may be configured accordingto one or more policies of the policy engine 236 of the appliance. Inother embodiments, the collection agent 304 transmits collectedinformation on the client 102 to the appliance 200. In one embodiment,the policy engine 236 of the appliance 200 uses the collectedinformation to determine and provide access, authentication andauthorization control of the client's connection to a network 104.

In one embodiment, the collection agent 304 is an end-point detectionand scanning program, which identifies and determines one or moreattributes or characteristics of the client. For example, the collectionagent 304 may identify and determine any one or more of the followingclient-side attributes: 1) the operating system an/or a version of anoperating system, 2) a service pack of the operating system, 3) arunning service, 4) a running process, and 5) a file. The collectionagent 304 may also identify and determine the presence or version of anyone or more of the following on the client: 1) antivirus software, 2)personal firewall software, 3) anti-spam software, and 4) internetsecurity software. The policy engine 236 may have one or more policiesbased on any one or more of the attributes or characteristics of theclient or client-side attributes.

The SSL VPN agent 308 is an application, program, process, service, taskor set of executable instructions for establishing a Secure Socket Layer(SSL) virtual private network (VPN) connection from a first network 104to a second network 104′, 104″, or a SSL VPN connection from a client102 to a server 106. In one embodiment, the SSL VPN agent 308establishes a SSL VPN connection from a public network 104 to a privatenetwork 104′ or 104″. In some embodiments, the SSL VPN agent 308 worksin conjunction with appliance 205 to provide the SSL VPN connection. Inone embodiment, the SSL VPN agent 308 establishes a first transportlayer connection with appliance 205. In some embodiment, the appliance205 establishes a second transport layer connection with a server 106.In another embodiment, the SSL VPN agent 308 establishes a firsttransport layer connection with an application on the client, and asecond transport layer connection with the appliance 205. In otherembodiments, the SSL VPN agent 308 works in conjunction with WANoptimization appliance 200 to provide SSL VPN connectivity.

In some embodiments, the acceleration program 302 is a client-sideacceleration program for performing one or more acceleration techniquesto accelerate, enhance or otherwise improve a client's communicationswith and/or access to a server 106, such as accessing an applicationprovided by a server 106. The logic, functions, and/or operations of theexecutable instructions of the acceleration program 302 may perform oneor more of the following acceleration techniques: 1) multi-protocolcompression, 2) transport control protocol pooling, 3) transport controlprotocol multiplexing, 4) transport control protocol buffering, and 5)caching via a cache manager. Additionally, the acceleration program 302may perform encryption and/or decryption of any communications receivedand/or transmitted by the client 102. In some embodiments, theacceleration program 302 performs one or more of the accelerationtechniques in an integrated manner or fashion. Additionally, theacceleration program 302 can perform compression on any of theprotocols, or multiple-protocols, carried as a payload of a networkpacket of the transport layer protocol.

In one embodiment, the acceleration program 302 is designed, constructedor configured to work with appliance 205 to provide LAN sideacceleration or to provide acceleration techniques provided viaappliance 205. For example, in one embodiment of a NetScaler appliance205 manufactured by Citrix Systems, Inc., the acceleration program 302includes a NetScaler client. In some embodiments, the accelerationprogram 302 provides NetScaler acceleration techniques stand-alone in aremote device, such as in a branch office. In other embodiments, theacceleration program 302 works in conjunction with one or more NetScalerappliances 205. In one embodiment, the acceleration program 302 providesLAN-side or LAN based acceleration or optimization of network traffic.

In some embodiments, the network optimization engine 250 may bedesigned, constructed or configured to work with WAN optimizationappliance 200. In other embodiments, network optimization engine 250 maybe designed, constructed or configured to provide the WAN optimizationtechniques of appliance 200, with or without an appliance 200. Forexample, in one embodiment of a WANScaler appliance 200 manufactured byCitrix Systems, Inc. the network optimization engine 250 includes theWANscaler client. In some embodiments, the network optimization engine250 provides WANScaler acceleration techniques stand-alone in a remotelocation, such as a branch office. In other embodiments, the networkoptimization engine 250 works in conjunction with one or more WANScalerappliances 200.

In another embodiment, the network optimization engine 250 includes theacceleration program 302, or the function, operations and logic of theacceleration program 302. In some embodiments, the acceleration program302 includes the network optimization engine 250 or the function,operations and logic of the network optimization engine 250. In yetanother embodiment, the network optimization engine 250 is provided orinstalled as a separate program or set of executable instructions fromthe acceleration program 302. In other embodiments, the networkoptimization engine 250 and acceleration program 302 are included in thesame program or same set of executable instructions.

In some embodiments and still referring to FIG. 3, a first program 322may be used to install and/or execute the client agent 120, or anyportion thereof, automatically, silently, transparently, or otherwise.In one embodiment, the first program 322 is a plugin component, such anActiveX control or Java control or script that is loaded into andexecuted by an application. For example, the first program comprises anActiveX control loaded and run by a web browser application, such as inthe memory space or context of the application. In another embodiment,the first program 322 comprises a set of executable instructions loadedinto and run by the application, such as a browser. In one embodiment,the first program 322 is designed and constructed program to install theclient agent 120. In some embodiments, the first program 322 obtains,downloads, or receives the client agent 120 via the network from anothercomputing device. In another embodiment, the first program 322 is aninstaller program or a plug and play manager for installing programs,such as network drivers and the client agent 120, or any portionthereof, on the operating system of the client 102.

In some embodiments, each or any of the portions of the client agent120—a streaming client 306, a collection agent 304, SSL VPN agent 308, anetwork optimization engine 250, acceleration program 302, andinterceptor 350—may be installed, executed, configured or operated as aseparate application, program, process, service, task or set ofexecutable instructions. In other embodiments, each or any of theportions of the client agent 120 may be installed, executed, configuredor operated together as a single client agent 120.

D. Systems and Methods for Using an SSL Session from a Pool of SSLSessions Shared Between Intermediaries

End-to-end secure communications between a client 102 and a server 106may be provided by an SSL session connection. The connection may beestablished across one or more intermediaries, such as networkappliances 200, between the client 102 and the server 106 in a networkedsystem. In some embodiments, multiple intermediaries may be configuredto provide data acceleration and/or other services between the server106 and the client 102. A pair of intermediaries providing dataacceleration between the pair of intermediaries may use a signalingtunnel between the pair of intermediaries to establish a secure channelfor communications.

Referring now to FIG. 4A, one embodiment of a system 400 for using a SSLsession from a pool of SSL sessions 477 shared between intermediaries200 is shown. In brief summary, the system shows a first intermediary200 a and a second intermediary 200 b processing a client request 405for a secure connection to a server 106. These intermediaries 200 canbe, or comprise features from any embodiment of the appliances 200described above in connection with FIGS. 1A-C, 2A and 3. The firstintermediary 200 a may be in communication with one or more clients 102while the second intermediary 200 b may be in communication with one ormore servers 106. In some embodiments, the client 102 may establish atransport layer connection with the server 106 for communications. Insome of these embodiments, the client 102 may establish a SSL sessionwith a first intermediary 200 a. The first intermediary 200 a issometimes referred to as a client-side intermediary 200 a. In some otherembodiments, the first intermediary 200 a may establish the SSL sessionwith the client 102, for example, responsive to a request 405 from theclient 102.

In some embodiments, the server 106 may establish a SSL session with asecond intermediary 200 b. The second intermediary 200 b is sometimesreferred to as a server-side intermediary 200 b. In some embodiments,the second intermediary 200 b may establish the SSL session with theserver 106, for example, responsive to a request from the client 102,server 106, and/or first intermediary 200 a. In another embodiment, oneor more SSL sessions with the server 106 may be established responsiveto the establishment of a signaling tunnel 450.

The client-side and server-side SSL sessions may be establishedconcurrently or at different times. The client-side and server-side SSLsessions may be established independently. In some embodiments, a pairof client-side and server-side SSL sessions may be established based onsome trigger, configuration or requirements, for example, responsive toa peer list 468. In some embodiments, the client-side and server-sideSSL sessions are established responsive to a same event. For example andin one embodiment, the client-side and server-side SSL sessions areestablished when a client registers with the system, e.g., the firstintermediary 200 a. In another embodiment, the client-side andserver-side SSL sessions are established when the first and secondintermediaries 200 are initialized or otherwise added to the network104. In still another embodiment, the client-side and server-side SSLsessions are established when the client 102 and/or the server 106 areadded to the network 104. In yet another embodiment, the client-side andserver-side SSL sessions are established when the first and secondintermediaries are identified to handle communications in relation tothe client 102 and/or the server 106. For example and in one embodiment,the client-side and server-side SSL sessions are established when thefirst and second intermediaries are identified in a peer list 468 thatpairs or otherwise groups a plurality of intermediaries forcommunications.

In some embodiments, one or both of the client-side and server-side SSLsessions are established in anticipation of communications between aclient 102 and a server 102. Establishment of one or both of theclient-side and server-side SSL sessions, in advance or in parallel withother segments of an end-to-end SSL session, may reduce the latencyand/or complexity of establishing the end-to-end SSL session. Theclient-side and server-side SSL sessions may share one or moreconfigurations, settings, attributes, identifiers, and/or otherinformation. These configurations, settings, attributes, identifiers,and/or other information may be determined, maintained, stored, and/ormanaged by one or more of: the client 102, server 106, firstintermediary 200 a, second intermediary 200 b and a storage device. Insome embodiment, a SSL session pool manager 466 determines, maintains,stores, and/or manages these configurations, settings, attributes,identifiers, and/or other information.

The first intermediary 200 a and/or the client 102 may establish aplurality of client-side SSL sessions between the first intermediary 200a and the client 102. A plurality of client-side SSL sessions related toone or more clients 102 is hereafter sometimes referred to as aclient-side SSL session pool. The second intermediary 200 b and/or theserver 106 may establish a plurality of server-side SSL sessions betweenthe second intermediary 200 b and the server 106. A plurality ofserver-side SSL sessions related to one or more servers 106 is hereaftersometimes referred to as a server-side SSL session pool.

The client 102 may generate and transmit a request 405 destined for theserver 106 to initiate communications. In some embodiments, the request405 may be a request for secure communications with the server 106. Therequest 405 may comprise any form or type of message, packet orcommunications, and may be encrypted and/or compressed. The request 405may be implemented in any type or form of communications protocol,including custom, proprietary and/or standard protocols. In oneembodiment, the request 405 is an unsecured communication, for example,to initiate secure communications with the server 106. In anotherembodiment, the request 405 is sent via a secured communicationschannel, such as within an SSL session established between the client102 and the first intermediary 200 a.

In some embodiments, the request 405 comprises a Signaling Helloprotocol message. The request 405 may identify a desired applicationprotocol. Further, the request 405 may include capability details, forexample, regarding the client 102. The request 405 may also be part of ahandshaking protocol, for example, a synchronization (SYN) signal ormessage. The request 405 may also comprise a request to initiate dataacceleration along the client-server network path, such as between thefirst and the second intermediaries 200.

The request 405 may initiate establishment of a transport layer (e.g.TCP) connection and/or a SSL session. In some embodiments, the request405 is intercepted or received by the first intermediary 200 a and maybe routed to the server 106. In one of these embodiments, the request405 is directed to the second intermediary 200 a. The secondintermediary 200 b may be identified by a peer list 468 a as pairedwith, or otherwise related to the first intermediary 200 a. In someembodiments, the request 405 is forwarded to the second intermediary 200b via a signaling tunnel 450. In other embodiments, the request 405initiates establishment of one or more signaling tunnels 450 between thefirst and second intermediaries. The request may initiate establishmentof an SSL session. The request may initiate establishment of a transportlayer connection between the client 102 and the server 106. Responsiveto the establishment of the transport layer connection, a securedsession (e.g., a SSL session) may be established.

In some embodiments, the request 405 comprises a request for informationrelated to the establishment of a connection to the server 106. Forexample and in one embodiment, the information requested may relate toone or more SSL sessions of a pool established between the secondintermediary 200 b and the server 106. This request 405 may be processedor handled by one or more pool managers 466.

In some embodiments, responsive the request 405, the first intermediary200 a determines if a signaling tunnel 450 is available between thefirst intermediary 200 a and the second intermediary 200 b. Thesignaling tunnel 450 may be any type or form of communications tunnel,channel, connection, session or link and may be implemented in one morecommunications protocol, including custom, proprietary and/or standardprotocols. In some embodiments, the signaling tunnel 450 is a controlchannel for, but not limited to, control, administrative, handshakingand/or initialization messages. The signaling tunnel 450 may support ortransport data transfer of different rates, including intermittent andcontinuous data transfer. In some embodiments, the signaling tunnel 450is distinguished from typical communications channels, such as thoseused to transport non-control messages. The signaling tunnel 450 may bea temporary tunnel or may be persisted after an SSL session isestablished.

The signaling tunnel 450 may be used to setup data acceleration, such asSSL acceleration, between the first intermediary 200 a and the secondintermediary 200 b. The signaling tunnel 450 may provide a securetunnel, including encryption and/or other security measures. In someembodiments, one or more signaling tunnels 450 are setup between peerintermediaries identified in a peer list 468. A peer list 468 may beconfigured on one or more intermediaries 200. Responsive to theconfiguration on an intermediary 200, the intermediary 200 may attemptto establish a signaling tunnel 450 with one or more of theintermediaries' peers. The peer list 468 may be configured by any means,such as by an administrator or a peer list management module or processthat manages some aspect of network traffic. The peer list 468 may beconfigured directly onto an intermediary 200 or may be communicated tothe intermediary, for example via a request (e.g., request 405). Thepeer list 468 for a first intermediary 200 a may be communicated fromanother intermediary 200 b, 200 c, and may be communicated via anexisting or established signaling tunnel 450.

The peer list 468 is sometimes referred to as a configuration list ofpeer intermediaries. In some embodiments, the peer list 468 indicatespairs or groups of trusted peers or intermediaries 200. Peercertificates, or SSL certificates, may be used by peer intermediaries200 to establish trust between the peer intermediaries 200. Theintermediaries 200 in a peer list 468 may be listed or specified usingany form or type of identifiers, such as IP addresses. Theintermediaries 200 may also be identified by domain name, such as FullyQualified Domain Name. The domain name of an intermediary 200 may beresolved by Domain Name System (DNS). If a request for SSL sessionestablishment is received by a first intermediary 200 a that has notbeen configured with a second intermediary 200 b in a peer list or thatdoes not have access to a peer list 468, the first intermediary 200 amay be responsible for authenticating the second intermediary 200 b. Thefirst intermediary 200 a may also be responsible for establishing asignaling tunnel 450 with the second intermediary 200 b. The firstintermediary 200 a and the second intermediary 200 b may initiate anupdate of a peer list 468, for example, responsive to authentication.This update may applied to one or both of the peer lists 468 of theintermediaries 200.

In some embodiments, the signaling tunnel 450 enables a pair ofintermediaries to authenticate each other. In addition, the signalingtunnel 450 can allow a pair of intermediaries 200 to communicate SSLspecific information. The signaling tunnel 450 can enable the pair ofintermediaries 200 a, 200 b, to setup a set of SSL state machine pairsfor establishing one or more SSL sessions between a client 102 and aserver 106. In some embodiments, the signaling tunnel 450 is used tocommunicate out-of-band messages, such as SSL session re-negotiationmessage and SSL shutdown messages. Intermediaries 200 may also use thesignaling tunnel 450 to communicate information about signaling agents,such as identifiers of agents, signaling tunnel internet protocols(IPs), and SSL acceleration specifics. These information may furtherinclude information to identify operational configurations or modes of apair of intermediaries, such as configurations for spoofing or splitproxy modes.

The signaling tunnel 450 may itself be a SSL connection between the pairof intermediaries 200. In some embodiments, establishment of thesignaling tunnel 450 may require SSL configuration information to beconfigured on the pair of intermediaries 200. The signaling tunnel 450may use any portion of existing infrastructure provided by a tunnelestablished between a certificate authority (CA) and an intermediary200. The signaling tunnel 450 may support an application to applicationprotocol capability for inter-protocol communications betweenintermediaries 200, or between an intermediary 200 and a CA.

The signaling tunnel 450 may be established using a plurality ofmethods. In one embodiment, the signaling tunnel 450 is established atinitialization time, for example, of one or both intermediaries 200 of apeer pair. In another embodiment, a signaling tunnel 450 is establishedresponsive to a new SSL connection request, for example initiated by aclient request 450. After the establishment of the signaling tunnel 450,the pair of intermediaries 200 may establish a pool of SSL contexts. ASSL context may include any of: infrastructure, configuration, settings,state machines, handshaking operations and protocols for setting up aSSL session and/or connection. In some embodiments, establishment of apool of SSL contexts allows for fast allocation of new SSL connectionsbetween a pair of intermediaries 200. One or more intermediaries 200associated with the pool of SSL contexts may manage this pool.Management of the pool of contexts may include, but are not limited to,allocation, cleanup, maintenance of SSL state machines and encryptionkeys. In some embodiments, the pool of SSL contexts is referred to as aSSL session pool 477.

In some embodiments, each intermediary 200 identified in a peer list 468may create a plurality of SSL state machines. In other embodiments, anintermediary 200 may create a plurality of SSL state machines regardlessof a peer list 468, for example, responsive to an SSL sessionestablishment request 405. An intermediary 200 may create a plurality ofSSL state machines corresponding to a plurality of SSL sessionsestablished between the intermediary 200 and one or more clients 102and/or servers 106. A mapping of the plurality of SSL state machines tothe plurality of SSL sessions may be described as a one-to-one orone-to-many relationship. A first intermediary 200 a may create a firstplurality of SSL state machines corresponding to a second plurality ofSSL state machines created by a second intermediary 200 b (for example,according to a peer list 468). A mapping of the first plurality of SSLstate machines to the second plurality of SSL state machines may bedescribed as a one-to-one or one-to-many relationship.

Responsive to a request 405 for establishment of a SSL session, a pairof SSL state machines can be selected from the first plurality andsecond plurality of state machines. In OpenSSL terminology, SSL statemachines may be referred to as SSL Objects. In some embodiments, each ofthe state machines may use the signaling tunnel 450 as a transportmechanism. Between a first and a second intermediary 200, the statemachines on one of these intermediaries 200 a may operate in “accept”mode. The state machines on the other intermediary 200 b may operate in“connect” mode. In some embodiments, a “connect” mode state machine mayconnect to a unique “accept” state machine.

An SSL handshake between a pair of state machines can be conducted overthe signaling tunnel 450. A first state machine at the firstintermediary 200 a and a second state machine at second intermediary 200b may use OpenSSL application programming interfaces (APIs) toencrypt/decrypt the data communicated via the signaling tunnel 450. Thefirst and second state machines may use a cipher pre-negotiated duringthe signaling tunnel establishment process to encrypt/decrypt the datacommunicated via the signaling tunnel 450. In some embodiments, uponcompletion of the SSL handshake, the transport mechanism for datatransfer may switch from the signaling tunnel 450 to the transport layer(e.g., TCP) connection. The first and second state machines may then usethe transport layer connection as the transport mechanism to sendencrypted traffic.

The signaling tunnel 450 may be used to communicate any further type orform of information between a pair of intermediaries 200 or SSL statemachines. In some embodiments, information 444 is transmitted in aresponse to the request 405. In other embodiments, information 444 istransmitted or exchanged responsive to establishment of the signalingtunnel 450. The information 444 may include one or more signaling IPaddresses. A signaling IP address may be an IP address for identifyingone of: an intermediary 200, a state machine, a client 102 and a server106. The information 444 may also include information associated withone or both SSL state machine pool and/or intermediaries 200, forexample:

-   -   1. Cipher List—The list of ciphers supported by an intermediary        200.    -   2. Pool Size—The size of the pool (for example, at        initialization time).    -   3. Free Pool Threshold—A threshold for initiating growth of a        pool if the free pool capacity falls below this threshold value.    -   4. Low Pool Usage Threshold—A threshold for initiating reduction        of a pool if pool usage falls below this threshold value (e.g.,        for a pre-determined amount of time).

In some embodiments, the information 444 may include SSL proxyparameters, such as for initializing and/or establishing an SSL session,which may include:

-   -   1. SSL Service Class—An indication of the service class for data        transfer, for example, including one or more bits that indicate        enabling/disabling of SSL acceleration.    -   2. Trusted CAs—A list of trusted certification authorities.    -   3. Private Key Store Table—A list of private keys for different        servers 106, client 102 and/or intermediaries 100.    -   4. SSL Service Class Table—A table or container including IP        Address and Port tuple information. In some embodiments, for        every tuple, the Table includes a list of proxy configuration        names and/or keys that references the Proxy Configuration Table.    -   5. Proxy Configuration Table—A table or container with entries        that includes:        -   a. Proxy Configuration Name—A primary Key        -   b. Virtual Server Name—An identifier for an associated            virtual server which may be used when a server name is sent            by the Client in a request 405 (e.g., via a Client Hello            Message).        -   c. Proxy Type—Identifies whether the SSL proxy type is of            Split or Spoofing type.        -   d. Client and Server Side Configuration Data—A configuration            data structure including:            -   Private Key Name—key names referenced from the Private                Key Store Table            -   Server Certificates—certificates of a server 106 or                virtual server.            -   Certificate Authority            -   Certificate Chain—RSA (Rivest, Shamir and Adelman)/DSA                (Digital Signature Algorithm) Formats for public key                cryptography.            -   SSL Protocol Version            -   Cipher List—ciphers available and/or negotiated by the                intermediaries 200.

In some embodiments, a first intermediary 200 a may be configured with alist of ciphers for encrypting and decrypting the traffic with a secondintermediary 200 b or vice-versa. A pair of intermediaries 200 (e.g.,peer intermediaries) may negotiate a cipher for encryption during thesignaling tunnel establishment. The negotiation may be initiated by arequest 405, such as a Signaling Hello Message. Upon completion of thenegotiation, the pair of intermediaries 200 can use the negotiatedcipher for encryption/decryption between the pair of intermediaries 200,which may or may not be limited for use in the signaling tunnel 450. Insome embodiments, one or more ciphers may be negotiated and/orconfigured for each connection segment between any two of: a client 102,a first intermediary 200 a, a second intermediary 200 b and a server106.

In addition to security provided by cipher, each intermediary 200 mayhave portions of data encrypted, stored and/or persisted in a storagedevice. The storage device may be, or include features of, anyembodiment of storage elements 128, 122, 140 described above inconnection with FIGS. 1D and 1E. In some embodiments, the storage deviceis a database computer (DBC). The storage device may also store thenetwork data history associated with the intermediary 200. The storagedevice may be provided by any network device and may reside in one ormore network devices, including but not limited to the intermediaries200, the client 102 and/or the server 106. The stored data may beencrypted on a per file basis. In some embodiments, the system mayencrypt whole disks, partitions, logical volumes, and files associatedwith the data. For example and in one embodiment, an intermediary 200may use a file to store the data in the Windows platform. In anotherembodiment, the intermediary 200 may store the data in a logical volumeunder a Linux platform. For example, dm-crypt may be used to encrypt thedata in Linux. In addition, a swap file may contain data that is pagedto a disk which may be used to support memory larger than thatphysically available from the storage device. This swap file may beencrypted for security.

Although passages in this disclosure may generally refer to statemachines, it should be understood that each state machine represents amodel of behavior implemented by a combination of hardware and software,and as such, any of the actions described herein by a state machine maybe performed by a module, component, and/or device of the correspondinghardware intermediary 200. In addition, a selection of a state machineor state machine pair may be equivalent to the selection of acorresponding or related SSL session from a SSL session pool 477. Forexample and in one embodiment, selection of a pair of state machinesfrom the respective state machine pools of the first and secondintermediaries 200 represents the selection of a SSL session from theserver-side SSL session pool 477 of the second intermediary 200 b.Furthermore, the pools of state machines and/or SSL session pools may bemaintained and/or managed by one or more pool managers 466.

In further details of FIG. 4A, a pool manager 466 may be provided atleast in part by the first intermediary 200 a, the second intermediary200 b and/or other network components. A plurality of pool manager 466may reside in one or more network components, and operate incommunication with one another. For example and in one embodiment, afirst pool manager 466 in the first intermediary 200 a may operate witha second pool manager 466′ in the second intermediary 200 b. By way ofillustration and not intended as a limitation, we will sometimes referto one or more pool managers 466 as a single pool manager 466.

A pool manager 466 may be implemented in hardware or a combination ofhardware and software. The pool manager 466 may be built and configuredfor supporting or providing SSL security features. The pool manager 466may include any module, script, program, agent, component or set ofexecutable instructions executing on one or more intermediaries 200. Thepool manager 466 may have components operating at one or more layers ofthe network stack, such as the transport layer. The pool manager 466 caninitiate and/or establish SSL sessions and connections within an SSLsession. The pool manager 466 may be initiated or otherwise renderedactive responsive to a request 405, a peer list, establishment of asignaling tunnel 450, or by other means. In addition, the pool manager466 may create, configure, maintain or otherwise manage a plurality ofSSL state machines. The pool manage 466 may also create, maintain andmanage a pool of SSL session keys and/or hash message authenticationcode (HMAC) keys between a pair of intermediaries 200 a, 200 b. In someembodiments, the pool manager 466 may coordinate or managecommunications via the signaling tunnel 450, for example, in theselection of a SSL session key from a key pool. Further, the pool manage466 may coordinate or manage communications regarding state machine,session identifier and/or cipher selection and matching.

In some embodiments, a pool manager 466 may maintain a plurality ofpools of state machines for each intermediary 200 (e.g., of a pair ofpeer intermediaries). A first of the plurality of pools of statemachines may be referred to as an owned pool. An owned pool is a poolthat is owned by the intermediary 200 from which it can allocate a statemachine for SSL connections. FIG. 4B illustrates one embodiment of astate machine for an owned pool 443. A second of the plurality of poolsof state machines may be referred to as a monitored pool 445. Amonitored pool 445 is a pool owned by the peer intermediary 200 b butmay be used by the intermediary 200 a to monitor the peer intermediary'sstate machine allocation. FIG. 4C shows embodiments of state machinesfor an SSL state machine identifier for an owned pool 443 and amonitored pool 445.

In some embodiments, each of the owned and monitored pools may maintaina plurality of lists. In one embodiment, the plurality of list includes,but is not limited to:

1. Free List: list of SSL state machines available for allocation;2. Allocated List: list of SSL state machines allocated to connections;and3. To-Be-Destroyed List: list of SSL state machines to be destroyed uponconfirmation, for example, from peer intermediary.

Each intermediary 200 a, via the pool manager, may create and maintainthe intermediary's owned pool and/or synchronize the intermediary'smonitored pool 445 with the peer intermediary 200 b's owned pool 443.The intermediary 200 a may use information transmitted via the signalingtunnel 450 by the peer intermediary 200 b in control or protocolmessages for the synchronization of the monitored pool 445. If anintermediary 200 detects that the signaling tunnel 450 between the peershas gone down, the state machine's owned pool may receive a destroyevent from the pool manager 466. Responsive to the destroy event, theowned pool 443 may be dissolved.

Pool Creation and Pool Growth

To establish a first pool of state machines, a first intermediary 200 amay determine an initial pool size (say ‘N’) and create N SSL statemachines. In some embodiments, an initial pool size may be based onplatform size, e.g., smaller initial pool sizes corresponding to smallerplatforms. In other embodiments, the system can maintain and update acounter value every time an SSL state machine pair is identified for usefrom the state machine pools. When an intermediary 200 a is initializedor reset, the intermediary 200 a can access the updated counter valueand begin with a configurable percentage of the updated counter value.In one of these embodiments, a counter value greater than apre-determined minimum number is used to determine the initial poolsize. For example and in one embodiment, if the saved counter value is75, the minimum pool size is 10 and the configurable percentage is 40%,then the initial pool size may be determined to be 30. This can be setas the initial counter value, or may be saved as the updated countervalue until a higher counter value (starting at 0) is reached.

In some embodiments, the first intermediary 200 a may determine theinitial pool size based in part on one or more of: available resources,including bandwidth and session count limits, information about theclient 102 and/or the server 106, and information from the request 405and/or configuration or user settings for the intermediary 200. Each SSLstate machine may be identified by a unique identifier. The pool managermay connect each of these state machines to the signaling tunnel 450 forpacket transport. The first pool of SSL state machines can then be movedto the “accept” state. The pool manager 556 may generate and send a poolupdate message to a second intermediary 200 b. The pool update messagemay include, but is not limited to, the following information:

1. a request identifier set to “Create Request”;2. a desired pool size of N; and3. a list of SSL state machine identifiers.

In some embodiments, a second intermediary 200 b (e.g., a peerintermediary) receives the pool update message over the signaling tunnel450. The second intermediary 200 b may create the required number of SSLstate machines to form a second pool of state machines. For example andin one embodiment, the second intermediary 200 b creates N SSL statemachines responsive to the pool update message. The second intermediary200 b can further generate and assign a unique identifier to each statemachine of the second pool. The pool manager 556 may associate a statemachine from the second pool with a state machine from the first pool.In some embodiments, the pool manager 556 may pair up the identifiers ofthe first and second pools of state machines by generating an identifierfor a state machine pair from the identifiers of each of the statemachine pair. For example, a combination of an identifier of a firststate machine from the first pool and an identifier of a second statemachine from the second pool can yield a unique identifier thatidentifies the SSL state machine pair comprising the first and secondstate machines. For example, if the first state machine identifier is‘1234’ and the second state machine identifier is ‘5678’, then the SSLstate machine pair may be identified by an identifier ‘12345678’, basedon concatenating the state machine identifiers.

The second intermediary 200 b may send a pool update response, in oneembodiment including but not limited to:

1. a request identifier set to “Create Complete”;2. a list of SSL state machine identifiers associated with the firstpool; an3. a list of SSL state machine identifiers associated with the secondpool.

Responsive to receiving the pool update response, the first intermediary200 a may pair and store the SSL state machine identifiers. The firstintermediary 200 a may also update its Free Pool List 471. The poolmanager 556 may connect, on behalf of the second intermediary 200 b, theSSL state machines of the second pool to the signaling tunnel 450 forsending packets over the signaling tunnel 450. In addition, the poolmanager 556 may move the state machines of the second pool to the“connect” state. In some embodiments, moving the state machines of thesecond pool to the “connect” state completes the SSL handshake betweenthe SSL state machine pairs. For a state machine pool of size ‘N’, N SSLhandshakes may be completed over the signaling tunnel 450. The sender ofthe pool update message (e.g., the first intermediary 200 a) may add theset of SSL state machine pair identifiers to the sender's Owned Pool443. The peer intermediary (e.g., second intermediary 200 b) maycorrespondingly add these identifiers to the peer intermediary'smonitored pool 445. Accordingly, the above-discussed mechanism of usingpool update messages and pool update responses enables growth in a statemachine pool.

In some embodiments, the system comprises a configurable parameter whichdetermines the Free Pool Threshold for purposes of managing ormaintaining a pool size. If the free pool capacity is below the FreePool Threshold, the pool manager 466 may increase the pool capacity upto a maximum quantum. For example and in one embodiment, this increaseoccurs by continuously doubling the pool capacity as long as the poolcapacity is below the maximum quantum and the Free Pool Threshold. Forexample, and in another embodiment, if we set the maximum quantum to 25,the Free Pool Threshold as 100 and initial pool size as 10, the pool mayprogressively grow as 20 (doubled), 40 (doubled), 65 (increase by maxquantum), 90 (increase by max quantum; below the Free Pool Threshold).In some embodiments, a pool of state machine pairs may be considered tohave two owners (the first intermediary 200 a and the secondintermediary 200 b). In these embodiments, the pool manager 466 may actto maintain or grow the pool size when one owner's pool shrinks. In someembodiments, the pool manager 466 may keep track of the rate ofreduction of a pool in deciding a growth factor for growing the pool.

SSL state machines from a client-side pool and a server-side pool may bepaired during creation or growth of SSL session pools. In someembodiments, the intermediary 200 having SSL state machines in the“connect” state may set the SSL session identifier of the intermediary200 to the SSL session identifier of the signaling tunnel 450. In someof these embodiments, the setting of the SSL session identifier of theintermediary 200 to the SSL session identifier of the signaling tunnel450 causes a key exchange process to be skipped. In some embodiments,skipping the key exchange process may speed up the establishment of theSSL session.

In some embodiments, each intermediary 200 may create a set of N memorybasic inputs/outputs (BIOS) corresponding to the N SSL state machines.Each SSL state machine may then connect to a memory BIO. In someembodiments, data that is to be sent over the TCP connection is writtento the write buffer (wbio) of the memory BIO. Incoming data on the TCPconnection may be read from the read buffer (rbio) of the memory BIO.For data transfer from a first intermediary 200 a to a secondintermediary (e.g., over a WAN), the first intermediary 200 a mayprocess a packet by separating the payload and header of the packet. Thefirst intermediary 200 a may determine the state machine pair identifierto identify the SSL state machine to transmit from. The firstintermediary 200 a may place the payload in the Memory BIO connected tothe identified SSL state machine. The first intermediary may encrypt thepayload and re-attach the header to form a new packet for transmission.In some embodiments, the header is in plaint text (i.e., not encrypted).

For an incoming packet, the receiving intermediary (e.g., secondintermediary 200 b) may process the packet to determine the statemachine pair identifier. Based on the state machine pair identifier, thereceiving intermediary can identify the SSL state machine for receivingthe packet. The identified state machine may separate the header andencrypted payload and store the payload in the Memory BIO connected tothe identified SSL state machine. The identified state machine maydecrypt the payload and re-attach the header to the decrypted payload toform a new received packet.

In further details of FIGS. 4B and 4C and in one embodiments, toestablish a SSL session, the second intermediary 200 b may allocate anSSL state machine pair from the Free List 471 on the secondintermediary's owned pool 443. The second intermediary 200 b may move astate machine pair on the second intermediary's owned pool 443 from theFree List 471 to the Allocated list 472. The second intermediary 200 bmay transmit a message (e.g., SYN-ACK message) that comprises theidentifier of this SSL state machine pair to the first intermediary 200a. The first intermediary 200 a can extract the identifier from themessage and move the corresponding state machine pair on the MonitoredPool 445 from the Free List 471 to the Allocated List 472. In FIG. 4C,this represents a state machine transition from “Free ID” to “AllocatedID”.

Pool Reduction

The pool manager 466 may set an active usage threshold of the SSLsession pool and track actual usage periodically. If the active usagedoes not get beyond the threshold value, the pool manager 466 may reducethe pool size by some predetermined or dynamically determinedpercentage. The pool manager may maintain usage statistics such as amaximum usage for each SSL session or intermediary 200, usage per timeperiod, memory usage for pools aggregated across one or more SSLsessions associated with an intermediary 200. In some embodiments, thenumber of state machines expiring or being destroyed may be small, e.g.,small compared to state machine growth.

To reduce or shrink an owned pool, an intermediary 200 a may identify anumber of SSL state machine pairs from the Free List 471 to remove.These SSL state machine pairs may be removed from the tail-end (or anyportions) of the Free List 471. The pool manager 556 may send a poolupdate message on behalf of the intermediary 200 a to the peerintermediary 200 b. The pool update message may comprise thecorresponding identifiers of the state machine pairs identified forremoval. The request identifier of the pool update message may be set to“Destroy Request”, indicating that state machine pairs are to beremoved. The intermediary 200 a may then move the identified SSL statemachine pairs to the To-Be-Destroyed List 473 on the intermediary'sowned pool 443. The peer intermediary 200 b may receive the pool updatemessage over the signaling tunnel 450. Responsive to the pool updatemessage, the pool manager 466 of the peer intermediary 200 b may movethe identified SSL state machines from the Free List 471 to theTo-Be-Destroyed List 473 on the monitored pool 445. The pool manager 466may send back a pool update response which includes the identifiers ofthe state machine pairs identified for removal. The request identifierof the pool update response may be set to “Destroy Complete” to confirmthat the removal update has been synchronized at the peer intermediary200 b (as reflected in the monitored pool 445). In some embodiments,responsive to receiving the pool update response, the pool manager 466of the intermediary 200 a may flush the To-Be-Destroyed List 473.

Expiration of SSL Sessions

In some embodiments, the SSL handshake between the SSL state machinesare completed before a SSL session key is allocated to TCP connections.In some embodiments, the same SSL session key is reused for multiple TCPconnections. To implement a renegotiation for SSL session keys, peerintermediaries 200 may exchange lifetime parameters for the SSL sessionkey. This exchange may occur during the establishment of the signalingtunnel 450. The lifetime parameter of each of the peer intermediary maydiffer in value. In one embodiment, the minimum of the two lifetimeparameter values may be computed and used for determining the SSLsession lifetime. In other embodiments, the maximum, average, or otherfunction of the lifetime parameter values may be used. Each SSL statemachine pair may be tagged with an expiry time based on the computedvalue. Each SSL state machine pair may periodically check for expirationof the SSL session key.

An intermediary 200 s may move expired state machines (i.e., SSLsessions) from the Free List 471 or Allocated List 472 to theTo-Be-Destroyed List 473 and send a pool update message to a peerintermediary 200 b. Responsive to the pool update message, the peerintermediary 200 b may delete the corresponding SSL state machines fromthe Free List on the peer intermediary's monitored pool 444 and send aconfirmation response. Responsive to the confirmation response, theintermediary 200 a may flush or empty its To-Be-Destroyed list 473.

In some embodiments, if the intermediary 200 a discovers expired SSLstate machines on its Allocated List 472, the pool manager 466 of theintermediary 200 a may wait until an existing SSL session or connectionis closed so that these state machines are returned to the Free List471. To avoid re-allocating a recently expired state machine, the systemmay check if the SSL state machine has expired before allocating it toan SSL session.

Referring now to FIG. 4D, a flow diagram depicts embodiments of stepstaken in a method 400 for using a Secure Socket Layer (SSL) session froma pool of SSL sessions shared between intermediaries 200. The methodincludes receiving, by a first intermediary, a peer list 468 including asecond intermediary (501). The first intermediary 200 a is incommunication with one or more clients and the second intermediary 200 bis in communication with one or more servers. The first intermediaryestablishes a signaling tunnel with the second intermediary (503). Apool manager of the second intermediary maintains information on one ormore SSL sessions of a pool established by a second intermediary with aserver (505). The first intermediary receives information on one or moreSSL sessions of a pool established by the second intermediary with aserver (507). The first intermediary receives a request from a client toestablish an SSL session with the server (509). The client is from theone or more clients in communication with the first intermediary. Thefirst intermediary identifies an SSL session from the pool of SSLsessions (511). The first intermediary establishes the SSL session withthe client responsive to the request (513).

Referring now to FIG. 4D, and in greater detail, the method includesreceiving, by a first intermediary, a peer list 468 including a secondintermediary (501). The first intermediary 200 a is in communicationwith one or more clients 102 and the second intermediary 200 b is incommunication with one or more servers 106. The first intermediary 200 amay receive the peer list 468 from one or more of: an administrator ofthe system 400, a second intermediary 200 b, a third intermediary 200 c,the client 102, a server 106, a storage device or other networkcomponent. In some embodiments, the administrator may configure the peerlist 468 into the first intermediary 200 a. In some embodiments, thefirst intermediary 200 a requests for a peer list 468 responsive to anevent, such as receipt of a request 405. In other embodiments, the firstintermediary 200 a creates a peer list 468 responsive to an event, suchas receipt of a request 405 (e.g., a SYN message). In some of theseembodiments, the first intermediary 200 a creates the peer list 468based on information included in the request 405. In still anotherembodiment, the intermediary 200 a receives the peer list 468 in therequest 405.

In some embodiments, the first intermediary 200 a may identify thesecond intermediary 200 b based on the peer list 468. The firstintermediary 200 a may identify the second intermediary 200 b as a peerintermediary 200 b, for example, a trusted intermediary 200 b. The firstintermediary 200 a may identify the second intermediary 200 b from aplurality of intermediaries 200, for example identified by the peer list468. The first intermediary 200 a may identify the second intermediary200 b based on a request 405 from the client 102, for example,identified by a signaling IP address in the request 405. For example andin one embodiments, the first intermediary 200 a may identify the secondintermediary 200 b based on the second intermediary's association with aserver 106 identified in the response 405. The first intermediary 200 amay determine if a signaling tunnel 450 to the second intermediary 200 bexists. If no signaling tunnel 450 exists, the first intermediary 200 amay send a response (e.g., a SYN-ACK) to a SYN request 405, without SSLoptions attached, to the client 102. In some embodiments, this initiatesa connection with the second intermediary 200 b without SSLacceleration.

In some embodiments, the first intermediary establishes a signalingtunnel 450 with the second intermediary (503). The first intermediary200 a may establish the signaling tunnel 450 in response to one or bothof: the peer list 468 and the request 405. In some embodiments, thesignaling tunnel 450 is established prior to receiving a request 405from the client 102. A pool manager 556 or other component of the firstand/or second intermediaries 200 may establish the signaling tunnel 450on behalf of, or based on the direction of the first and/or secondintermediaries 200. The first intermediary 200 a may establish thesignaling tunnel 450 as a secure connection with the second intermediary200 b. The first intermediary 200 a may establish the signaling tunnel450 for exchanging control messages with the second intermediary 200 b.The first intermediary 200 a may establish the signaling tunnel 450 tosetup an SSL session connection with the second intermediary 200 b.

The first intermediary 200 a may initiate authentication of the secondintermediary 200 a.

The first intermediary 200 a may negotiate a cipher or encryption methodwith the second intermediary 200 b. The first intermediary 200 a and thesecond intermediary 200 b may select from a pool of ciphers orencryption keys configured in one or both of the intermediaries 200. Oneor both intermediaries 200 may encrypt some or all data exchangedbetween the intermediaries 200 using the cipher negotiated over thesignaling tunnel 450.

The first intermediary 200 a may establish one or more SSL sessions withone or more clients 102, for example, responsive to the establishment ofthe signaling tunnel 450 and/or the peer list 468. The secondintermediary 200 b may establish one or more SSL sessions with one ormore servers 106, for example, responsive to the establishment of thesignaling tunnel 450 and/or the peer list 468. In one embodiment, thesecond intermediary 200 b establishes one or more SSL sessions with eachof a plurality of servers 106 for one or more pools of SSL sessions. Thefirst intermediary 200 a may establish one or more SSL sessions witheach of a plurality of clients 102 for one or more pools of SSL sessions477. Responsive to establishment of the signaling tunnel 450, one orboth of the first intermediary 200 a and the second intermediary 200 bmay create one or more SSL state machines. A pool manager 466 of thefirst intermediary 200 a may associate a first (or client-side) pool ofSSL state machines with the one or more SSL sessions established betweenthe client 102 and the first intermediary 200 a. A pool manager 466 ofthe second intermediary 200 b may associate a second (or server-side)pool of SSL state machines with the one or more SSL sessions establishedbetween the server 106 and the second intermediary 200 b.

In some embodiments, a pool manager of the second intermediary 200 b,maintains information on one or more SSL sessions of a pool 477established by a second intermediary 200 b with a server (505). A poolmanager 466 of the first intermediary 200 a may maintain information onone or more SSL sessions of a pool 477 a established by the firstintermediary 200 a with the client 102. One or more pool managers 466may maintain information on the first and/or second pool of statemachines 477. One or more pool managers 466 may maintain information ona pool of ciphers or encryption keys configured on one or bothintermediaries 200. In addition, the one or more pool manager 466 maymaintain any of these information on one or more storage devicesdescribed above in connection with FIG. 4A.

The pool manager 466 may maintain statistics of current and past SSLsessions between the intermediaries, including usage statistics of eachSSL session. The pool manager 466 may maintain pool thresholds, poolsize counters, rate of change of pool size, and growth quantum of eachSSL session pool 477. The pool manager 466 may maintain, update and keeptrack of the owned pool 443 and/or monitored pool 445 of eachintermediary 200. The pool manager 466 may maintain, update and keeptrack of the Free Pool 471, Allocated pool 472, and To-Be-Destroyed Pool473 of an intermediary 200. The pool manager 466 may maintain and keeptrack of the state machine pair identifiers of SSL sessions, whetheractive or expired.

In further details of FIG. 4D, the first intermediary 200 a receives,via the signaling tunnel 450, the information 444 on the one or more SSLsessions from the pool manager 466 (507). A pool manager 466 a of thefirst intermediary 200 a may receive the information 444 from a poolmanager 466 b of the second intermediary 200 b. The first intermediary200 a may query from the second intermediary 200 b information on theone or more SSL sessions of the pool 477. The second intermediary 200 bmay forward to the first intermediary 200 a information on the one ormore SSL sessions of the pool 477. The first intermediary 200 a maycommunicate with a storage device (e.g., maintained by the secondintermediary 200 b) to access the information on the one or more SSLsessions 477.

The first intermediary 200 a may receive session specific data for theone or more SSL sessions of the pool 477. For example and in oneembodiment, one of a plurality of SSL sessions and/or state machines onthe server side may be identified by the pool manager 466 with whichsession specific data is gathered and/or transmitted. The one of theplurality of SSL sessions and/or state machines may be identifiedrandomly or based on historical records and/or the request 450 from theclient 102.

In some embodiments, the information 444 received may include any of theinformation 444 described above in connection with FIG. 4A-5C. Theinformation 444 may be transmitted and/or exchanged prior to receipt ofa request 450 from the client 102. In some embodiments, the information444 may be transmitted and/or exchanged responsive to the peer list. Theinformation 444 may also be transmitted and/or exchanged responsive toestablishment of the signaling tunnel 450. The second intermediary 200 bmay encrypt some or all of the information 444 prior to transmission tothe first intermediary 200 a. The second intermediary 200 b may encryptsome or all of the information 444 using a cipher or encryption keynegotiated with the intermediary 200 a. The first intermediary 200 areceiving the information 444 may decrypt the information 444, e.g.,using the cipher or encryption key negotiated with the intermediary 200a.

The second intermediary 200 b may further compress or other process theinformation 444 before transmission to the first intermediary 200 a. Thesecond intermediary 200 b may send the information 444 over one or moremessages via the signaling tunnel 450. The second intermediary 200 b maysend the information 444 including an SSL state machine pair identifier.The second intermediary 200 b may send the information 444 in responseto a SSL pool update message from the first intermediary 200 a. Thesecond intermediary 200 b may send the information 444 in a SSL poolupdate response to an SSL pool update message.

In some embodiments, the first intermediary receives a request from aclient to establish an SSL session with the server (509). The firstintermediary 200 a may receive the request 405 to establish a SSLsession with the server 106. The first intermediary 200 a may interceptthe request as a request 405 from the client 102 directed to the server106. The first intermediary 200 a may receive the request 405 responsiveto establishment of a SSL session between the client 102 and the firstintermediary 200 a. The first intermediary 200 a may receive the request405 to establish a second SSL session with a second server 106 b. Thefirst intermediary 200 a may receive the request 405 after the signalingtunnel 450 has been established. The first intermediary 200 a mayreceive the request 405 after some information 444 have been transmittedto the first intermediary 200 a.

The first intermediary 200 a may receive the request 405 as part of aclient Hello message and/or a SYN message. The first intermediary 200 amay receive the request 405 as part of a handshaking process to initiateand/or establish a SSL session. The first intermediary 200 a may receivethe request 405 with SSL related options. The first intermediary 200 amay receive the request 405 including one or more signaling IPaddresses, e.g., identifying one or more server 106. The firstintermediary 200 a may receive the request 405 including a request fordata acceleration, compression and/or encryption. The first intermediary200 a may receive the request 405 including at least a portion of a peerlist for the first intermediary 200 a.

Responsive to the request 405, the first intermediary 200 a may identifythe second intermediary 200 b for establishment of a connection. If thesecond intermediary 200 a is not in a peer list 468 a of the firstintermediary 200 b, the first or second intermediaries may initiate anupdate of one or both of their peer lists. If a signaling tunnel 450does not yet exist between the first and the second intermediaries, thefirst intermediary 200 a may initiate establishment of a signalingtunnel 450 in accordance to the process steps described above inconnection with step 403. This may be optionally followed by anyembodiment of process steps described above in connection with steps 405and/or 407.

Responsive to the request 405, the second intermediary 200 a may sendadditional information to the first intermediary 200 a and/or the poolmanager 466. This information sent may supplement the information 444sent earlier. This information may include SSL Proxy setup information.For example and in one embodiment, this information is exchanges as partof a SSL proxy handshake to determine the type of proxy to beestablished, i.e., Split or Spoofing. Furthermore, this information mayinclude any embodiment of information 444 described above in connectionwith FIG. 4A. In addition, information such as SSL session key, IPaddress-Port tuple, Virtual Server Name, and other client and/or serverside configuration details may be exchanged between the first and secondintermediaries. In one embodiment, the configuration information for aspoofing proxy includes a server private key which references an SSL KeyStore Table. In another embodiment, the configuration information for asplit proxy includes server certificate, certificate chain and otherdata configured in an SSL Key Store Table.

In further details of step 411, the first intermediary 200 a identifiesan SSL session from the pool of SSL sessions 477. The first intermediary200 a may request for an available SSL session from the pool of one ormore server-side SSL sessions. The first intermediary 200 a may requestfor an available SSL state machine from the pool of server-side SSLstate machines 477. The first intermediary 200 a may request for an SSLstate machine in the Free List 471 of the second intermediary's ownedpool 443. In some embodiments, the pool manager 556 identifies an SSLsession from the pool of SSL sessions 477. The pool manager 556 mayidentify an SSL session from the server-side SSL sessions. The poolmanager 556 may identify a SSL state machine from the server-side SSLstate machine pool. The pool manager 556 may further identify a SSLstate machine from the client-side SSL state machine pool.

The pool manager 556 may identify a pair of SSL state machines from theserver-side and client-side SSL state machine pools. The pool manager556 may identify the pair of SSL state machines using an SSL statemachine pair identifier. The pool manager 556, the first intermediary200 a and/or the second intermediary 200 b may determine an SSL sessionfrom the server-side SSL sessions based on one or more of: theidentified server 106, the identified SSL state machines from theserver-side and client-side SSL state machine pools, the request 405,the information 444, and other information exchanged. The pool manager466 or first intermediary 200 a may identify to the second intermediary200 a, use of the SSL session from the pool of one or more SSL sessions.This identification may be communicated to the second intermediary 200 bas part of handshaking communications for SSL session establishment.

In some embodiments, a handshaking process takes place for pairing up aclient-side state machine with a server-side state machine for SSLsession establishment. The second intermediary 200 a may select a SSLstate machine from the Free List 471 of the second intermediary's ownedpool 443. The second intermediary 200 a may compute a hash messageauthentication code (HMAC) of the selected state machine's identifierusing a HMAC key negotiated during establishment of the signaling tunnel450. The second intermediary 200 a may append the HMAC and theidentifier to a message (e.g., attached as a TCP option in a SYN-ACKmessage) to the first intermediary 200 a. The message may be transmittedalong with other SSL related options and information described above.

The first intermediary 200 a may receive the message with theidentifier. The first intermediary 200 a may compute a HMAC of theidentifier using the pre-negotiated HMAC key. The first intermediary 200a may verify the HMAC against that received in the message. If the HMACvalidates against that received in the message, the first intermediary200 a may update the first intermediary's monitored pool 445 inaccordance with the selected the SSL state machine. In some embodiments,if the HMAC does not match that in the message, the first intermediary200 a may not forward the message to the client 102. The server mayeventually time out and resend another message with the same or anotheridentifier. This process may be repeated until a valid HMAC is received,or until the connection is reset by the server 106. The pool manager 466may determine a state machine pair identifier from the validatedidentifier. The pool manager 466 may identify the client-side statemachine based on the state machine pair identifier.

In some embodiments, the first intermediary establishes the SSL sessionwith the client responsive to the request (513). The pool manager 466may establish an SSL session with the second intermediary 200 b onbehalf of the first intermediary 200 a via the identified pair of SSLstate machines. An SSL session may be established responsive to thevalidated pair of state machines. The pool manager 466 may move theidentified pair of SSL state machines into the respective AllocatedLists 472 of the intermediaries' owned pools 443. The secondintermediary 200 b may configure the SSL session between theintermediaries to have the same SSL session identifier of the identifiedSSL session with the server 106. The second intermediary 200 b mayconfigure the SSL session between the intermediaries to have the sameSSL session key of the identified SSL session with the server 106. Thefirst intermediary 200 a may configure the client-side SSL session tohave the same SSL session identifier of the identified SSL session withthe server 106. The first intermediary 200 a may configure theclient-side SSL session to have the same SSL session key of theidentified SSL session with the server 106. The first and/or secondintermediaries 200 may connect the client 102 and server 106 via asingle SSL session established via the client-side, server-side andintermediary SSL connection segments.

The first and second intermediaries may determine whether to acceleratedata transfer across the intermediaries 200. The first and secondintermediaries may determine whether to accelerate data transfer basedon information exchanged between the first and second intermediaries200. In some embodiments, the pool manager 466 pairs up the client-sideand server-side state machines if one or both of the intermediaries 200are able to support data acceleration. In other embodiments, the poolmanager 466 pairs up the client-side and server-side state machines forSSL session establishment regardless of whether one or bothintermediaries 200 are able to support data acceleration.

It should be understood that the systems described above may providemultiple ones of any or each of those components and these componentsmay be provided on either a standalone machine or, in some embodiments,on multiple machines in a distributed system. In addition, the systemsand methods described above may be provided as one or morecomputer-readable programs or executable instructions embodied on or inone or more articles of manufacture. The article of manufacture may be afloppy disk, a hard disk, a CD-ROM, a flash memory card, a PROM, a RAM,a ROM, or a magnetic tape. In general, the computer-readable programsmay be implemented in any programming language, such as LISP, PERL, C,C++, C#, PROLOG, or in any byte code language such as JAVA. The softwareprograms or executable instructions may be stored on or in one or morearticles of manufacture as object code.

While the invention has been particularly shown and described withreference to specific embodiments, it should be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the following claims.

1. A method for using a Secure Socket Layer (SSL) session from a pool ofSSL sessions shared between intermediaries, the method comprising: a)receiving, by a first intermediary, information on one or more SSLsessions of a pool established by a second intermediary with a server,the first intermediary in communication with one or more clients and thesecond intermediary in communication with one or more servers; b)receiving, by the first intermediary, a request from a client toestablish an SSL session with the server; and c) identifying, by thefirst intermediary, an SSL session from the pool of SSL sessions; and d)establishing, by the first intermediary, the SSL session with the clientresponsive to the request.
 2. The method of claim 1, wherein step (a)further comprises establishing, by the secondary intermediary, apredetermined one or more SSL sessions with the server to form the pool.3. The method of claim 1, wherein step (a) further comprisesestablishing, by the second intermediary, one or more SSL sessions witheach of a plurality of servers for one or more pools of SSL sessions. 4.The method of claim 1, wherein step (a) further comprises forwarding, bythe second intermediary, to the first intermediary information on theone or more SSL sessions of the pool.
 5. The method of claim 1, whereinstep (a) further comprises querying, by the first intermediary, from thesecond intermediary information on the one or more SSL sessions of thepool.
 6. The method of claim 1, wherein step (a) further comprisesreceiving, by the first intermediary, session specific data for the oneor more SSL sessions of the pool.
 7. The method of claim 1, wherein step(b) further comprises intercepting, by the first intermediary, therequest of the client communicated to the server.
 8. The method of claim1, wherein step (c) further comprises requesting, by the firstintermediary, an available SSL session from the pool of one or more SSLsessions.
 9. The method of claim 1, wherein step (c) further comprisesdetermining, by the first intermediary, an available SSL session fromthe information on the one or more SSL sessions of the pool.
 10. Themethod of claim 1, further comprising identifying, by the firstintermediary to the second intermediary, use of the SSL session from thepool of one or more SSL sessions.
 11. A system for using a Secure SocketLayer (SSL) session from a pool of SSL sessions shared betweenintermediaries, the method comprising: a first intermediary receivinginformation on one or more SSL sessions of a pool of SSL sessions, thefirst intermediary in communication with one or more clients; a secondintermediary in communication with one or more servers, the secondintermediary communicating the information on the one or more SSLsessions of the pool of SSL sessions established by the secondintermediary; wherein the first intermediary receives a request from aclient to establish an SSL session with the server, identifies an SSLsession from the pool of SSL sessions, and establishes the SSL sessionwith the client responsive to the request.
 12. The system of claim 11,wherein the secondary intermediary establishes a predetermined one ormore SSL sessions with the server to form the pool.
 13. The system ofclaim 11, wherein the second intermediary establishes one or more SSLsessions with each of a plurality of servers for one or more pools ofSSL sessions.
 14. The system of claim 11, wherein the first intermediaryqueries from the second intermediary information on the one or more SSLsessions of the pool.
 15. The system of claim 11, wherein step the firstintermediary receives session specific data for the one or more SSLsessions of the pool.
 16. The system of claim 11, wherein the firstintermediary intercepts the request of the client communicated to theserver.
 17. The system of claim 11, wherein the first intermediaryrequests an available SSL session from the pool of one or more SSLsessions.
 18. The system of claim 11, wherein the first intermediarydetermines an available SSL session from the information on the one ormore SSL sessions of the pool.
 19. The system of claim 11, wherein firstintermediary identifies to the second intermediary use of the SSLsession from the pool of one or more SSL sessions.
 20. The system ofclaim 11, wherein the first intermediary communicates with one or moreclients via a first local network, the second intermediary communicateswith the one or more servers via a second local network, and the firstintermediary and second intermediary communicates via a wide areanetwork.